Note: Descriptions are shown in the official language in which they were submitted.
CA 022~0~60 1998-11-09
RECORDING DEVICE HAVING SHORT DATA WRITING TIME
This is a divisional of Canadian Patent Application
Serial No. 2,065,832 filed April 10, 1992.
BRIEF DESCRIPTION OF THE DRAWINGS:
Fig. 1 illustrates the constitution of an array-
type recording device according to the prior art;
Fig. 2 illustrates the constitution of a preferred
embodiment of an array-type recording device according to
the present invention;
Fig. 3 is a flow chart showing one operation of the
embodiment shown in Fig. 2;
Fig. 4 is a flow chart showing another operation of
the embodiment shown in Fig. 2;
Fig. 5 is a flow chart showing still another
operation of the embodiment shown in Fig. 2; and
Fig. 6 illustrates the arrangement of data within a
disk unit in the embodiment shown in Fig. 2.
BACKGROUND OF THE INVENTION:
1. Field of the Invention
The present invention relates to a recording device
and an array-type recording device for use as a storage
system in a computer, and, more particularly, to an
improvement in the performance and reliability of a disk
drive system having a plurality of disk units arranged in
an array.
2. Description of the Prior Arts
A variety of literatures and patents have disclosed
disk systems comprising a plurality of disk units arranged
in an array. Of these literatures, an article titled "A
Case for Redundant Arrays of Inexpensive Disks (RAID)",
CA 022~0~60 1998-11-09
- la -
Proc. ACM SIGMOD Conf., Chicago, IL, June, 1988 published
by The Berklay Institute of the University of California
describes a method of dramatically improving the
reliability of stored data. The article proposed
classifying a method of improvement in data reliability
into five levels. These range from a conventional mirror
disk system to a block interleave parity system. Outlines
of the respective levels are described as follows.
CA 022~0~60 1998-11-09
RAID level 1
This is of a conventional mirror (shadow) system
wherein identical data are stored in two groups of disk
units. The system according to RAID level 1 has been
generally employed in systems requiring a high level of
reliability. However, redundancy is considerable and the
cost for unit capacity is accordingly high.
RAID level 2
A hamming code type which is used in a DRAi~l is
applied to this level. Data are stored in data disks for
a redundancy group in a bit interleaving manner. In the
meantime, in order to enable correction of one bit error to
be e.Yecuted, ECC codes are written in a plurality of check
disks for one group (one group comprising 10 to 25 sets of
disks). ~our check disks are required for ten sets of data
disks. Redundancy is considerable.
RAID level 3
Predetermined parity disks are used and data
are recorded in data disks of a certain group in a byte
interleaving manner. Since error positions can be located
by an ECC for each drive, one set of parity disks may be
needed. This system is suitable for a high speed transfer
by synchronously rotating spindles.
RAID level 4
Predetermined parity disks are used and data are
recorded in data disks of a certain group in a block
interleaving manner. A difference between RAID level 4
and RAID level 3 is that a different interleave unit is used
in level 4. More specifically, since data are recorded in
each block, this system is suitable for a case where a small
volume of data is frequently accessed.
RAID level 5
Unlike the afore-said levels 3 and 4, predetermined
parity disks are not provided. Parity data are dispersedly
stored, i.e., striped in constituent disks. As a conse-
quence, at the time of writing operation, parity disks
are not subjected to concentrated loads and IODS may be
CA 022~0~60 1998-11-09
increased (The greater the rate of writing, the more
advantageous will be this system compared to RAID level 4).
Performance at the time of use as well as a capacity
efficiency are desirable.
An example of a conventional array-type recording
device having redundancy is disclosed in Japanese Patent
Laid-Open Publication No. 236714/90 wherein a system and
method of driving array-type disks are disclosed. In this
system, a redundancy level and a logical number of component
disk units viewed from a host computer can be selected.
~ ith reference to the striping of parity data,
Japanese Patent Laid-Open Publication No. 293356/87
discloses a data protection mechanism and a method thereof.
Fig. 1 illustrates the constitution of a conventional
array-type recording device which has been disclosed
in afore-said Japanese Patent Laid-Open Publication No.
236714/90. In Eig. 1, the reference numeral 1 designates
a host computer; 2 a host interface (hereinafter called
Host I/F) which serves as a buffer between host computer 1
and an array controller 13; 3 a microprocessor adapted to
control the whole array controller 13; 4 a memory; 5 an ECC
engine adapted to generate redundancy data and reconstruct
data; 6 a data path commonly connected to host I/F 2,
microprocessor 3, memory 4 and ECC engine 5; 7 a CE panel;
and 8a through 8e channel controllers. CE panel 7 and the
plurality of channel controllers 8a - 8e are connected to
data path 6. The reference numerals 9a - 9e designate dlsk
units; and 10 channels, through which the plurality of disk
units 9a - 9e are connected to channel controllers 8a - 8e;
11 stand-by disks; 12 spare channels, through which
plurality of stand-by disks 11 are connected to channel
controller 8; and 13 an array controller for controlling
plurality of disk units 9a - 9e and stand-by disk 11.
Operation of the illustrated recording device
will next be explained. In Fig. 1, data are recorded and
reproduced by host computer 1 through host I/F 2. Upon
CA 022~0~60 1998-11-09
storage of data, commands and data from host computer 1 are
stored in memory 4 by way of data path 6. Upon reproduction
of data, the data stored in memory 4 is transferred to host
computer 1 by way of host I/F 2.
Operation of the recording device in the case of RAID
level 5 will now be explained. The data stored in memory 4
is divided by microprocessor 3 into data blocks, and disk
units in which data is to be written and disk units in which
redundancy data is to be written are determined. In RAID
level 5, since old data stored in a data block corresponding
to the writing operation is required for updating redundancy
data, a reading operation is executed prior to the writing
operation. Data is transferred between memory 4 and channel
controllers 8, 8a - 8e by way of data path 6, and redundancy
data is generated by ECC enFine 5 synchronously with the
transfer of data.
For example, in the case of writing data of 10~
byte long, assuming that a data block is set at 512 byte
long, the data of 1024 byte long is striped into two blocks
whereby writing-data disk units 9a, 9b and a redundancy-data
disk unit 9e are determined. Next, under the control of
microprocessor 3, ECC engine 5 is activated and a command to
read out old data for computing redundancy data is provided
to channel controllers 8a, 8b and 8e to which data disk
units 9a, 9b and redundancy-data disk unit 9e are connected.
After reading the old data out of data disk units 9a, 9b
and redundancy-data disk unit 9e, new data is written in
data disk units 9a, 9b in accordance with a command from
microprocessor 3, and updated redundancy data generated by
ECC engine 5 is written in redundancy-data disk unit 9e.
Then, the completion of the data writing operation is
reported to host computer 1. As described above, upon
writing data, old data must be read out in advance for the
purpose of generating redundancy data. resulting in a longer
processing time.
ReadinF out data will next be explained. When a
data reading command is issued from host computer 1, the
CA 022~0~60 1998-11-09
data block and the data disk unit in which relevant data is
stored are computed by microprocessor 3. For example, if
relevant data is stored in disk unit 9c, a command to read
the data is issued to channel controller 8c to which disk
unit 9c is connected. When the reading of the data from
disk unit 9c is completed, the read data is transferred to
memory 4 and the completion of reading the data is reported
to host computer 1.
Reconstruction of data at the time of occurrence
~f abnormality and reconstruction of data in stand-by
disks will next be explained. Reconstruction of data
is executed when, for example, the reading of data out
of disk unit 9c becomes impossible. In such a case, data
are read by microprocessor 3 from all the disk units of a
redundancy group which include the data blocks to be read
out by microprocessor 1 and the data of the data blocks
corresponding to the data which were unable to be read
out are reconstructed by ECC engine.
For example, if the redundancy group includes disk
units 9a, 9b, 9c and 9e, data blocks are read from disk
units 9a, 9b, and 9e and data are reconstructed in disk
unit 9c by ECC engine 5. The reconstructed data are then
transferred to memory 4 and the completion of data reading
operation is communicated to host computer 1. It is
understood that, even if it becomes impossible to read
out data due to an abnormality in a disk unit, data can
be reconstructed, resulting in the enhancement of data
storage reliability.
Reconstruction of data may be executed when, for
example, disk unit 9c becomes disabled. In this case, data
is read out by microprocessor 3 from all the disk units of
the redundancy group which include the data stored in disk
unit 9c, and data for disk unit 9c ls reconstructed by ECC
engine 5. The reconstructed data ls reconstructed in any
of the stand-by disks.
CA 022~0~60 1998-11-09
If the redundancy group is composed, for example, o~
disk units 9a, 9b, 9c and 9e, then data are read out from
disk units 9a, 9b and 9e, while data for disk unit 9c is
reconstructed by ECC engine 5. The reconstructed data is
written on any one of stand-by disks 11, while the data for
disk unit 9c is reconstructed in stand-by disk 11. In this
way, disk unit 9 which has been disabled may be replaced
with stand-by disk 11. It is to be noted, however, that,
during the replacement of disk unit 9c with stand-by disk
11, if any abnormality occurs in stand-by disk 11, such a
replacement process becomes complicated. Furthermore, since
such a replacement process is executed while the system is
in operation, the performance of the system will be degraded
during such a replacement process.
Since a conventional array-type recording device
is constituted such as described above, the prior art
device has serious problems in that, due to the necessity
of reading out data in advance for generating redundancy
data at the time of a data writing operation even in a
normal operation of the system, a processing time becomes
correspondingly slower.
The conventional device has a further problem in
that, during a process of replacement of disks in the case
of abnormality, if a stand-by disk used for replacement is
damaged, the performance of the system is further degraded.
The conventional device has still another problem
in that a possibility of a fault existing in channels to
which constituent disks are connected is not taken into
consideration.
SUMMARY OF THE INVENTION:
The present invention has been proposed to eliminate
the problems as described above, and an object of the
present invention is to provide a recording device and an
array-type recording device whlch improve a processing time
at the time of data writing operation.
A further object of the present invention is to
provide a reliable recording device and a reliable array-
CA 022~0~60 1998-11-09
type recording device which make it possible to detect
abnormality of stand-by disks prior to a replacement
process and further take into account any fault in channels
to which constituent disk units are connected.
The present invention according to the first aspect
provides a recording device including:
(a) an interface section serving as an interface
with a main unit such as a host computer;
(b) a recording means for recording data;
(c) a redundancy providing means for providing
redundancy for recorded data; and
(d) a control section for causing data to be
recorded in the recording means in accordance with a data
recording request from the main unit by way of the
interface section, said control section adapted to report
to the main unit the completion of data recording operation
by way of the interface section and cause redundancy data
provided by the redundancy providing means to be recorded
in the recording means.
In a further embodiment, this aspect of the
present invention provides a recording device, comprising:
an interface section for providing an interface with a main
unit such as a host computer so as to receive a data
recording request having first data; a recording means for
recording data; a redundancy providing means for providing
redundancy data for the first data; command means for
storing the data recording request, the command means
having a non-volatile memory for holding the data recording
request; and a control section for causing the recording
means to record the first data in accordance with the data
recording request, said control section being adapted to
report to said main unit a completion of the data recording
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request by way of said interface section and having means
for causing the redundancy data to be recorded in the
recording means after the completion is reported to said
maln unlt.
In this way, since the control section is designed
to report the completion of operation prior to the writing
of redundancy data in response to a writing request from
the main unit, a writing process time can be shortened.
The present invention according to the second
aspect provides an array-type recording device including:
(a) an interface section for serving as an
interface with a main unit such as a host computer;
(b) a recording means having a plurality of
recording sections arranged in an array for recording data;
(c) a non-volatile memory for storing
information; and
(d) a control section for causing a recording
request from the main unit by way of the interface section
to be recorded in the non-volatile memory before reporting
to the main unit the completion of data recording operation
by way of the interface section, and for causing data to be
recorded in any one of the recording sections of the
CA 022~0~60 1998-11-09
recording means in accordance with the recording request
stored in the non-volatile memory.
In this way, the control section causes data to be
written into the non-volatile memory in response to a data
writing request from the main unit and reports to the main
units the completion of data writing operation, thereby
shortening a writing process time.
The present invention according to the third aspect
provides a recording device including:
1(a) a recording means having a plurality of
recording sections arranged in an array for recording data;
(b) a redundancy providing means for generating
redundancy data in accordance with recorded data; and
(c) a control section for causing data to be striped
and recorded in at least one recording section of the
recording means, and for altering a recording section for
writing data in accordance with the number of recording
sections which have already recorded the striped data
and the number of recording sections in which new data
are written to cause obtained data to be provided to the
redundancy providing means for generating redundancy data.
In this way, at the time of writing data, since the
control section alters recording sections which read out
data first and which are necessary for generating redundancy
data in accordance with the number of recording sections
subJected to writing operation, a fewer number of first
reading recording sections necessary for generating
redundancy data may be read out, whereby a reading time
may be saved, resulting in quick generation of redundancy
data from the redundancy providing means.
The present invention according to the fourth aspect
provides an array-type recording device including:
(a) a recording means having a plurality o-f
recording sections arranged In an array for recording data;
35(b) a plurality of data transfer means connected to
the recording sections of said recording means; and
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_g_
(c) a control section for selecting another data
transfer means through which data are transferred, when an
access through one of the plurality of data transfer means
to the recording means is in error.
In this way, the data transfer means connects the
recording sections with the array controller by way of a
plurality of channels, and, if an access to a recording
section from the array controller via one of the channels
fails, the control section is designed to provide an access
to the recording section by way of another channel, whereby
system reliability may be enhanced. More specifically,
since each recording section is connected via a plurality
of channels to the array controller, even if access through
one channel to the recording section fails, access through
another channel to the recording section is possible,
thereby enhancing system reliability.
The present invention according to the -fifth aspect
provides a recording device including:
(a) a recording means having a plurality of
recording sections arranged in an array for recording data;
(b) a plurality of data transfer means connected to
the recording sections of the recording means; and
(c) a control section for selecting an unused
data transfer means for data trans-fer when one of the
plurality of data transfer means ls already occupied.
In this way, the data trans-fer means connects the
recording sections with a plurality of channels, and, when
access is made from the array controller to a recording
section by way of one of the channels, if that channel
is occupied by an access to other recording section, the
control section causes access to be made to the recording
section by way of another channel, whereby accessibility
may be enhanced. More specifically, since each recording
section is connected by way of a plurality of channels,
if a channel connected to a certain recording sectlon is
occupied and access to the recording section connected to
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-10--
the occupied channel is made, the control section identifies
an unused channel so as to enable access to the recording
section.
The present invention in accordance with the sixth
aspect provides a recording device including:
(a) recording sections for recording data;
(b) alternative recording units usable in place o~
the recording sections; and
(c) a maintenance diagnosis means for diagnosing
the alternative recording units to decide whether the
alternative recording units can be used or not.
In this way, the maintenance diagnosis means is
designed to periodically or non-periodically make diagnosis
of such alternative recording units replaceable with the
recording sections in the case of fault in any recording
section, and detect abnormality of the alternative recording
units, consequently, the alternative recording units can
be used in the case of abnormality of any of the recording
sections and disables the faulty recording sections so
as to separate them from the system, thereby improving
reliability.
The present invention according to the seventh aspect
provides a recording device including:
(a) recording sections for recording data;
(b) alternative recording units usable in place o-f
the recording sections;
(c) an error recording section for recording error
information at the time of recording data in and reproducing
data from recordin~ sectlon: and
(d) a maintenance diagnosis means for deciding
whether any recording section should be replaced with the
alternatLve recording units or not in accordance with the
error informatlon recorded in the error recording means.
In this manner, the error recording means is designed
to collect and record error information when the system
is in operation, and the maintenance diagnosis means is
designed to decide if any recording section in which an
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error exceeding a predetermined level has occurred is
faulty, whereby a faulty recording section is replaced
with alternative recording units and the faulty recording
section is separated from the system. Therefore, there
is no possibility of concurrent faults occurring in
a plurality of recording sections, thereby improving
a system reliability.
The present invention according to the eighth aspect
provides an array-type recording device including:
(a) a recording means having a plurality of
recording sections arranged in an array for recording data;
(b) alternative recording units usable in place of
the recording sections;
(c) a control section for causing data to be
striped, recorded in and reproduced from the recording
sections, and for causing data in the recording section to
be replaced with the alternative recording unit at the time
of an access to the data recorded in the recording section.
In this way, the control section is designed, when
any recording section is damaged and the damaged recording
section should be replaced with any alternative recording
unit while the system is in operation, reconstructed
and unreconstructed areas when access is made to the
unreconstructed area of the faulty recording section or
when access is made to an area of another recording section
of the same redundancy group involved in the unreconstructed
area of the faulty recording section. ~s a result, the
entire process of completing the data reconstruction may
be shortened. ~urthermore, if Ihe completion of data
reconstruclion is reported to the main unit before the
~Q reconstruction in the alternative recording unit, a response
time can be made shorter.
The present lnvention according to the nlnth aspect
provides an array-type recordin~ device including:
(a) a recordir.g means having a plural~ty of
~ recording sectlons arranged Ln an array for recording data;
_ _ _
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- lla-
(b) a control section causing data to be striped,
recorded in and reproduced from the recording sections;
(c) alternative recording units usable in place of the
recording sections; and
(d) a means for recording correct data of said recording
means in any of the alternative recording units.
In this way, when a recording section is damaged and the
faulty recording section is replaced with an alternative
recording unit, if data can be read out of a faulty record-
ing section without error, the read data is used for data
reconstruction. Consequently, data reconstruction can be made
faster than in the case of utilizing data which has been
reconstructed from data stored in other recording sections of
the redundancy group.
The present invention according to the 10th aspect
provides an array-type recording device including: means for
receiving a data recording request having first data from a
main unit; a recording means for recording data; a
redundancy providing means for providing redundancy data for
the first data; command means for non-volatilely storing the
data recording request; means for causing the recording
means to record the first data and in response thereto
provide a completion indication to the main unit; and means
for receiving the data recording request from the command
means and in response thereto causing the recording means to
record the redundancy data after the completion is reported
to the main unit.
In this way, information as to which data block is to be
written in is stored in memory for the preparation of
abnormality of the power source in response to a data
writing request from the main unit and completion of the
data writing operation is reported to the main unit prior to
the writing of the redundancy data.
The present invention according to the 11th aspect
provides an array-type recording device including: means for
receiving a data recording request having first data from a
main unit; a recording means for recording data; command
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means for non-volatilely storing the data recording request;
a cache for storing the first data non-volatilely; means for
reporting a completion to the main unit upon storing the
command in the command means and the first data in the
cache; and means for causing the first data stored in the
cache to be recorded in the recording means in accordance
with the data recording request stored in the command means.
In this way, information as to which data block is to
be written in, and the data to be written, is stored in
memory for the preparation of abnormality of the power
source in response to a data writing request from the main
unit.
The present invention according to the 12th aspect
provides an array-type recording device including: an
interface section for providing an interface with a main
unit such as a host computer so as to receive a data
recording request having first data; a recording means for
recording data, the recording means having a plurality of
areas corresponding to a plurality of redundancy groups; a
redundancy providing means for providing redundancy data for
the first data; command means for storing the data recording
request, the command means having a non-volatile memory for
holding the data recording request; and a control section
for causing the first data and the redundancy data to be
written to an area of the recording means corresponding to
one of the plurality of redundancy groups, said area having
a subarea which contains no data, the control section further
causing the first data and the redundancy data to be
written to the subarea which contains no data.
In this way, information as to which data block is to
be written in is stored in memory for the preparation of
abnormality of the power source in response to a data writing
request from the main unit to write to an area of a recording
means which contains no data.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS:
Embodiments of the present invention will now be
explained by referring to Fiq. 2 through Fig. 6. In Fig. 2,
the reference numeral l designates a host computer; 2 a host
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-12-
I/F (an interface section) which serves as a buffer between
host computer 1 and an array controller 13; 3 a microproces-
sor which controls the whole array controller 13; 4 a memory
in which programs, data and the like used in microprocessor
3 are stored; 5 an ECC engine (a redundancy providing means)
adapted to detect errors in data which pass through data
path 6 and encode and decode the corrected data; 8a through
8e channel controllers which provide control between the
array controller and disk units; 9 disk units (recording
sections) in which data are stored; lOa and lOb channels; 11
stand-by disks (alternative recording units) which are spare
disk units; 14 a command/status memory comprising a RAM
which hold commands transmitted from host computer 1 and
a status representing a processing state; 15 a cache which
holds data sent from host computer 1 and data read from disk
units 9, command/status memory 14 and cache 15 being backed
up by a memory back-up mechanism 16 comprising a secondary
power source such as a battery; 18 a power source control
device for supplying power and providing control to disk
units 9 and stand-by disks 11; 20 a maintenance diagnosis
processor adapted to monitor, as a maintenance diagnosis
means, array controller 13, disk units 9 and stand-by disks
11 and cause error information to be stored in an error
storage means 19 in case of abnormality and to be displayed
on a display panel 21; and 22 a remote communicating device
adapted to inform a maintenance center (not shown) of error
information or the like. Microprocessor 3 and memory 4~form
a control section 23 and microprocessor 3 is operated by
programs and data stored in memory 4 so as to control array
controller 13 and the entire system.
Operation of the device shown in Fig. 2 will now be
e.Yplained. Fig. 3 is a flow chart showing operation of the
device illustrated in Fig. 2. When the array-type recording
device receives a writing request from host computer l,
microprocessor 3 causes data to be read from data blocks ot
writin~-data disk units and data blocks of redundancy-data
disk unlts in accordance wlth a predetermined data arr.~yin~
form.
. ,
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--13 -
For example, if data disk unit 9a and redundancY disk
unit 9e are designated, ECC engine 5 is activated under the
control of microprocessor 3 and a command to read old data
used for the purpose of computing redundancy data is issued
to channel controllers 8a and 8e to which data disk unit 9a
and redundancy data disk unit 9e are respectively connected.
After old data have been read out from data disk unit 9a and
redundancy data disk unit 9e, new data is written into data
disk unit 9a by a command from microprocessor 3 and new
redundancy data produced by ECC engine 5 (obtained, for
example, in RAID level 5, by an exclusive-OR operation of
old data Do read from and new data Dn stored in data disk
unit 9a and old redundancy data Po read from redundancy data
unit 9c, that is, Pn = Do ~ Dn ~ Po where ~ represents an
exclusive-OR operation) is written in redundancy data disk
unit 9e. In this case, when the writing of the new data is
finished, microprocessor 3 informs host computer 1 of the
completion of data writing operation prior to the completion
of writing the new redundancy data. Subsequently, if the
writing of the redundancy data is not yet completed, micro-
processor 3 causes such a writing operation to be continued
as a background process.
In this manner, since the completion of data writing
operation is reported to host computer 1 prior to the
completion of writing new redundancy data in a redundancy
disk~unit, seemingly high speed writing operation may be
achieved.
Information as to which block data is to be written
in is stored in command/status memory 1~ for the preparation
of abnormality of the power source as well as the system.
Even if an abnormality occurs in the power source or ~he
system, redundancy data may be generated and written in a
redundancy disk unlt at the time of system restart by data
from other disk unlts of the redundancy group in accordance
with the information stored in command/status memory l~
backed up by memory back-up mechanism 16, ~vhereby the
wri~ing operatlon may be completed. The Lnformation on
command/status memory 1~ Ls canceLled when a redundancy
CA 022~0~60 l998-ll-09
--14--
data writing process is completed. It is to be noted that,
iE command/status memory 14 becomes full, the writing of
redundancy data is completed prior to other processes.
In this embodiment, information as to which block
data is to be written in is stored in command/status memory
14. However, such information as well as redundancy data
may be stored in memory 14. In the latter case, redundancy
data may be directly written in a redundancy disk unit
at the time of system restart based on the information
stored in command/status memory 14 and it is unnecessary
to generate redundancy data based on data from other disk
units of the redundancy group as in the above-described
embodiment.
As explained above, since the completion of data
writing operation is reported to host computer 1 prior
to the completion of writing new redundancy data in a
redundancy disk unit, a seemingly high speed writing
operation may be achieved, and, even if an abnormality
occurs in the power source and the system, a writing
operation can be completed, resulting in no contradiction
of data.
As explained above, according to the present
invention, there is provided an array-type recording device
which has a plurality of disk units arranged in an array
for storing and reproducing data for a computer system,
the array-type recording device having redundancy providing
means for providing redundancy data for data to be writtJen
by a computer into the array-type recording device and
being capable of reporting to the computer the completion
of data writing operation prior to the completion of writing
redundancy data generated by the redundancy providing means.
Fig. 4 is a flow chart showing other operation
performed in the device shown in Fig. 2. When the array-
type recording device recelves a writing request from host
computer 1. microprocessor 3 causes the command to be stored
in command/status memory 14. After havin~ stored data
subsequently sent from host computer 1 Ln cache 15. micro-
processor 3 reports to host computer l ~he completion of
CA 022~0~60 1998-11-09
-15--
data writing operation. Subsequently, microprocessor 3
causes data to be written into a disk unit in accordance
with the command as a background process.
In this operation, task execution status which is
necessary for writing data and status information sent
from a disk unit are stored in command/status memory 14 in
preparation for a power source failure or a system error.
Should any abnormality occur in the power source or the
system, the writing of data into a disk unit may be actually
completed after a system restart in accordance with informa-
tion stored in a cache 15 and command/status memory 14
backed up by memory back-up mechanism 16. The information
stored in command/status memory 14 is cancelled upon
completion o-f writing all data.
It is to be understood that if command/status memory
14 becomes full, the writing of data may be actually com-
pleted prior to other processes. In the case where cache 15
becomes full, FIFO may be used alternatively.
It is also to be noted that, upon receiving a command
from host computer 1, it is decided if writing command
information in a block of the same redundancy group as
the read block is included in command/status memory 14, and
if such information is decided to be included in memory 14,
the writing of such information is actually completed before
other processes.
In this way, the completion of writing operation is
reported to host computer 1 before actually writing dat~
into a disk unit, whereby a seemingly high speed writing
operation may be attained. Further, even in the case of
occurrence of failure in the power source and the system,
the writing of data can be definitely completed, thus
avoiding any contradiction of data.
As explained above, according to the present
invention, there is provided an array-type recording device
having a plurality of disk units arranged in an array for
storing and reproducing data in a computer system, the
array-type recording device including a redundancy providing
means for providing redundancy and a non-volatile memory.
CA 022~0~60 1998-11-09
In the case where data from the computer are written in
the array-type recording device, the writing of data in the
non-volatile memory is reported to the host computer as the
completion of writing the data in the recording device.
According to the present invention, there is also
provided an array-type recording device having a non-
volatile memory for storing commands from a computer system
and internal processing state of the array-type recording
device, wherein, when any abnormality occurs in the array-
type recording device, a command from the computer system
may be executed again or data may be reconstructed in
accordance with the information stored in the non-volatile
memory.
The non-volatile memory may comprise a RAM backed
up by a secondary power source such as a battery, thereby
enabling a part of RAM memories in the recording device
can be utilized as the non-volatile memory. That is, no
additional non-volatile memory will be required, and the
disk drive device can be fabricated inexpensively and
easily.
It is to be understood that, in stead of constituting
command/status memory 14 and cache 15 with RAM, they can be
also constituted with normal non-volatile memories such as
EEPROMs.
Although command/status memory 14, cache 15 and
memory 4 are separate in the embodiment shown in Fig. 2,
they can be made of sections of one or more memories.
In RAID levels 4 and 5, when data is written, old
data to be updated is read out of a data disk unit and
a redundancy disk unit, and, after the generation of new
redundancy data, new data and the new redundancy data are
written. However, in case that the size o-f data to be
written is too large, such data occupies a pluralitY ~f
data dlsk units when written. In such an instance, new
redundancy data can be possibly generated faster if data
is read from a disk unlt of the same redundancy group in
whlch no data ls written.
For example, in the case of a system allowing at
CA 022~0~60 l998-ll-09
--17--
least one damaged disk unit in a redundancy group to be
recovered, assuming that the redundancy group includes
(N + 1) disk units and a piece of data is written in M
disk unLts, it is normally necessary to read old data
from (M + 1) disk units for generating the redundancy data.
By comparing the old data with new data, ECC engine 5 can
generate new redundancy data.
As another method of generating redundancy data,
it is possible to generate such data by reading data from
disk units of the same redundancy group in which no data is
written. In this case, data are read out of (N - M) disk
units. In this example, microprocessor 3 in control section
23 compares (1~ + 1) with (N - M) and exec-utes a processing
based on one of the two methods by which data is written in
fewer number of disk units.
As explained above, according to the present
invention, there is provided an array-type recording device
having a control section capable o-f altering disk units
of which data are to be read out first for generating
redundancy data depending on the number of writing disk
units at the time of data writing operation.
In the device illustrated in Fig. 2, channel lOa
and channel controller 8a constitute the first data
transfer means, while channel lOb and channel controller 8b
constitute the second data transfer means. Disk unit 9a
is connected to two channels lOa and lOb. If access to
the disk unit through one of the channels lOa becomes e~ror,
such access is switched to the other of the channels lOb,
thereby enabling access to be completed. In this way, the
occurrence of errors in channels may be avoided.
There may be more than t-vo channels per channel
controller and a plurality of channels may be controlled
by one channel controller.
As e.Yplained above, according to the present
invention, there is provided an array-type recording device
wherein disk units arranged in an array arc connectcd to
an array controller by way of a pLurality of channels. and
wherein lf access from the array controller ~o any disk
CA 022~0~60 l998-ll-09
--18--
unit by way of one of the channels results in error, another
access to the disk unit can be achieved through another
channel.
Channel lOa and channel controller 8a constitute the
first data transfer means, while channel lOb and channel
controller 8b constitute the second data transfer means.
Disk unit 9a is connected to two channels lOa and lOb.
Control section 23 may select and alter a channel path
during the operation of the system. If one of the channels
lOa is occupied and one of the disk units connected to
channel lOa has been got access, when an access request
for other disk unit connected to channel lOa is made,
control section 23 enables access to this other disk unit
by utilizing channel lOb. Thus, since control section 23
is capable of arbitrarily selecting and altering channels
depending on the status thereof, an access time can be
shortened, whereby the performance of the system may be
enhanced.
As explained above, according to the present
invention, there is provided an array-type recording device
capable of selecting or altering, out of a plurality of
channels, a channel path for enabling access to a disk unit
connected to an array controller by way of a plurality of
channels during operation of the system.
The array-type recording device illustrated in Fig. 2
may have a plurality of stand-by disks 11 which replace any
damaged disk units. It is, however, to be noted that, ajs
stand-by disks may be damaged during rest, these stand-by
disks 11 are periodically or irregularly diagnosed in
a background operation under the control of maintenance
diagnosis processor 20 (maintenance diagnosis means) shown
in ~Ig. 2. As a result, lf any abnormality is detected
by the diagnosis processor, such a faulty stand-by disk is
disabled and separated from the system. For this reason,
such a situation that a d~sk unlt is damaged during use and
a stand-by disk to replace is also damaged can be avoided.
Thus, an available stand-by disk is always ready for use.
Maintenance dlagnosls means 20 includes a means for
CA 022~0~60 1998-11-09
--19--
selecting and setting the number of stand-by disks and,
using the result of periodical or irregular diagnosis of
disk units, can reduce the number of stand-by disks when the
system is found to be highly reliable, but can increase the
number of stand-by disks when the system reliability drops.
It is also possible to hold such stand-by disks in an
immediately available state or "hot" state. Alternatively,
they can be held in a "cold" state, that is power supply
is off except when the diagnosis is conducted or replacement
of the stand-by disk is executed, or held in combination of
the "hot" and "cold" states. If the stand-by disk un-its are
held in the "cold" condition, the stand-by disk units can
be energized in accordance with a command from maintenance
diagnosis processor 20 during diagnosis by way of power
supply control device 18, thereby enabling the diagnosis.
After the completion of diagnosis, the stand-by disk units
are deenergized to be held in the cold condition.
Holding the disk units in a cold condition reduces
power consumption and prevents any shortening of the disk
unit life due to rotation of the disks under an energized
condition.
Alternatively, the disk units are held in an
energized state but the disks of the disk units are not
rotated according to commands from channel controllers
8a - 8e in a normal condition. During diagnosis, the disks
are rotated, and after the diagnosis, the disks are again
stopped from rotating, thereby enabling a longer life. J
In this case, no special H/W is required for turning ON
and OFF the power supply for the disk units.
As e,Yplained above, according to the present
invention, there is provided an array-type recording device
having stand-by disk units which may replace faulty disk
units if constituent disk units fail, and a maintenance
diagnosis means for diagnosing the stand-by disk units
periodically or irregularly and for, when any abnormality
is detected by the diagnosis, disabling and separating the
stand-by disks from the system. ~ means for selecting and
. . _, ., . . _
CA 022~0~60 1998-11-09
--20--
setting the number of stand-by disk units may be provided
further.
The stand-by disk units may be held in a "hot"
condition in which they are always available, in a "cold"
condition in which power supply is turned off except during
the time of diagnosis and replacement. or in combination of
the "hot" and "cold" conditions.
The stand-by disks which have been held in a "cold"
condition are energized at the time of diagnosis to conduct
diagnosis and deenergized after the completion of diagnosis
to be held in the "cold" condition.
Alternatively, the stand-by disk units which are held
in a "cold" condition are held energized but the disks of
the disk units are not rotated in a normal state. The disks
are rotated during diagnosis and stopped rotation again
after the completion of the diagnosis.
In the array-type recording device illustrated in
Fig. 2, maintenance diagnosis processor 20 is adapted to
collect error information on constituent disk units during
the operation of the system and store the information in
error storage means 19 comprising a magnetic disk unit and
the like. As illustrated in Fig. 5, if any error exceeding
a predetermined level occurs in a certain disk unit,
the disk unit is predicted to be a possible faulty disk
unit, and is replaced with a stand-by disk (by means of
a background process or a ~oreground process), and the
possible ~aulty disk unit is separated from the system.
This ~act is exhibited on operation display panel 21.
Replacement o~ a disk unit with a stand-by disk is
controlled by microprocessor 3 during the operation of
the system by setting a replacement completion time
depending on system performance requirements or a pluralLty
of preferential replacement levels. Such a replacement
process may be e,Yecuted reducing any load imposed on the
system by selecting a replacement completion time or any
one of preferent~al replacement levels.
In addition to dlsplayLng a system status on
operation dlspl,~y panel ~1. a repl,~cement process.
CA 022~0~60 l998-ll-09
--21--
a separation process and other status may be communicated
to a maintenance center (not shown) by remote communicating
device 22 as fault information. This arrangement enables
quick maintenance such as exchange of separated disk units
to be executed, whereby such a problem as shortage of stand-
by disks may be prevented.
Maintenance diagnosis processor 20 may be substituted
for a maintenance diagnosis program performed by micro-
processor 3.
As explained above, accordin~ to the present
invention, there is provided an array-type recording device
having an error information storage means adapted to collect
and store error information on constituent disk units during
system operation, and a maintenance diagnosis means adapted
to decide that a disk unit in which an error exceeding a
predetermined level occurs is a possible faulty disk unit,
replace the possible faulty unit with a stand-by disk unit
and separate the possible faulty disk unit from the system.
The array-type recording device may further include
a means for replacing a faulty disk unit with a stand-by
disk unit during the operation of the system and a means
for setting a replacement completion time in accordance
with a system requirement or a plurality of preferential
replacement process levels.
It is also possible to provide a remote communicating
device which is capable of communicating replacement
execution information or fault information of the array-'type
drive device with a maintenance center.
RAID level 5 in the case of allowing merely one
faulty disk unit will next be explained with reference to
~ig. 6. Disk devices 9a - 9e constitute a redundancy ~roup.
If disk device 9b is damaged, it is replaced by stand-by
disk 11. In stand-by disk 11, data is reconstructed
sequentially from D1. When access is made to the data
associated with unreconstructed data. the reconstruction
of data may also be performed.
~ or example, ln the condition shown in ~ig. 6, il'
a request is made to read data 21, the data D"0, D2~'. D"3
CA 022~0~60 1998-11-09
-22-
and redundancy data P5 are read out to reconstruct data
D21 which is in turn written in stand-by disk 11 and is
transferred. At this time, after data D21 is reconstructed,
and before data D21 is written in stand-by disk 11, the
completion of data transfer and process is reported to host
computer 1. Subsequently data D21 is written in stand-by
disk 11 and reconstructed, whereby a rapid response may be
attained.
If a request for writin~ to data D21 is made, data
D20, D22, D23 are read out along with a new data D21 and
new redundancy data P5 ls generated. Those new redundancy
data P5 and new data D21 are written respectively into
disk unit 9e and stand-by disk 11, there~y attaining data
reconstruction. Even before the writing of new data D21
into stand-by disk 11 is completed, the completion of
writing operation may be reported to the host computer
at the time of the completion of writing new redundancy
data P5, whereby a rapid response may be realized.
When a request for reading data D17 is made, after
data D17 is read out and transferred to host computer 1,
data P4, D18 and D19 are read out and used, along with
D17, to reconstruct data D16 which is then written in
disk unit 11.
Furthermore, when a request for writing data D17 is
made, old data D17 and old redundancy data P4 are read out
to generate new redundancy data P4. Then new data D17 and
new redundancy data P4 are written. In this respect, wh~en
the writing of both new data is completed, the completion
of writing operation is reported to host computer 1, thereby
realizing a rapid response. Data D18 and D19 are read out
and used, along with data D17, to reconstruct data D16.
Then, data D16 is written in stand-by disk 11.
It is to be noted that an access to such recon-
structed data as data D6 may be made in a similar manner
as access to normal data.
It is also to be noted that even if the wrLtlng Oe
data into a stand-by disk faLls, data can be reconstructed
CA 022~0~60 1998-11-09
--23--
by using data read from other disk units of the same
redundancy group.
In this way, by reconstructing data in stand-by disk
unit 11 by taking into consideration access to data from
host computer 1, a part of reading and writing processes
for a reconstructing process may be performed with reading
and writing processes accompanied with access to data from
host computer 1, whereby the entire process can be reduced
as compared to the case in which a reconstructing process
is executed independently of access to data from host
computer 1.
As described above, according to the present in-
vention, there is provided an array-type recording device
wherein if a constituent disk unit is damaged and the
faulty disk unit is replaced by a stand-by disk during the
operation of the system, an unreconstructed area may be
reconstructed at times when access to the unreconstructed
area of the faulty disk unit is made, or when access to
an area of another disk unit of the same redundancy group
which is involved in the unreconstructed area of the faulty
disk unit, the unreconstructed area can be reconstructed.
If the above access is made for the purpose of
reading data, a report as to transfer of data and the
completion of reading process is made to the host computer
when all the data to be read out are prepared, and there-
after data are reconstructed. On the other hand, if the
above access is made for the purpose of writing data, a i
report as to the completion of writing process is made
to the host computer when the writing of data into disk
unit other than a stand-by disk in a redundancy group
which replaces a faulty disk unit is completed, and then
a reconstructing process is executed.
The present invention has been described with respect
to the case of a failure ln one disk unit. ~owever, data
can be reconstructed taking into consideration access to
a disk unit constituting the same redundancy group, even
if a failure in a plurallty of dlsk unlts is allowed by
the degree of redundancy.
CA 022~0~60 1998-11-09
-24-
In the array-type recording device shown in Fig. 2,
when any of disk devices 9a - 9e is damaged and the faulty
disk unit is to be replaced by a stand-by disk, if the
faulty disk unit includes any data area from which data may
be read out without errors, then the data read out of such
an area is written in stand-by disk 11 for reconstruction.
This may be executed by maintenance diagnosis processor 20
or microprocessor 3.
For example, even if scratches are formed across
a plurality of tracks on a disk in a disk unit, resulting
in a soft crash state, the data stored on the remaining
portions of the tracks may be read out. If a faulty disk
unit includes any area from which data can be read out
without errors, quicker reconstruction may be realized
by utilizing data read out of such an area rather than by
reading data from another disk units of the same redundancy
group. However, data corresponding to such areas as may
cause any error in data may be reconstructed by reading
data from other disk units of the same redundancy group.
As described above, according to the present
invention, there is provided an array-type recording device
having a replacing means for, if a constituent disk unit
is damaged and such a faulty disk unit is to be replaced by
a stand-by disk, if the faulty disk unit includes any area
from which data can be read out without any error, utilizing
the data read from such an area, and, utilizing instead
of data corresponding the areas other than the above are~a,
data reconstructed from data of other disk units of the
redundancy group including the faulty disk unit.
Although an example of an array-type disk drive
device has been described with reference to the drawings,
the present invention can be implemented in a variety of
manners. ~or example, an array-tYPe recording device may
be constructed on the basis of other RAID levels 1 - 5.
