Electrical computers and digital processing systems: memory – Storage accessing and control – Control technique
Reexamination Certificate
2000-03-23
2004-06-29
Gossage, Glenn (Department: 2187)
Electrical computers and digital processing systems: memory
Storage accessing and control
Control technique
C711S114000, C711S168000
Reexamination Certificate
active
06757797
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a copying method between logical disks, disk storage system and storage medium for copying between logical disks, and in more particular to a copying method, disk-storage system and storage medium that makes immediate access of a logical disk in response to a copy command possible.
2. Prior Art
A logical disk is a disk that appears to be unrelated to physical restrictions imposed by a physical disk. A logical disk can be constructed from a plurality of physical disk devices, or from one physical disk with a plurality of logical disks. The kind of disk used is determined by the parameters of capacity and performance.
This typical system is called RAID (for example 0, 1, 0+1, 3, 5) rank or RAID group.
Copying between logical disks is used as a backup for saving data as well as other uses. For example, executing a test while continuing work. In this case, the logical disk that is used for work is copied and the copy-destination logical disk is used by the test system. By doing this, the work being performed using the copy-source logical disk is not affected even if data are damaged by the test system that uses the copy-destination logical disk.
Also, a logical disk can be used in online work by copying the logical disk used in online work and using the copy-destination logical disk in batch processing. By doing this, the performance of the online work that uses the copy-source logical disk is not affected by the batch processing.
Many cases such as these which require copying between logical disks are increasing. However, work must be stopped while copying the logical disk. For example, it can take one hour to copy 9 Gbytes. In 24-hour continuous operating conditions of recent years, it is desirable to make the work stop time as close to zero as possible by making the copy time as close to zero as possible.
FIG. 13
to
FIG. 16
are drawings explaining the prior art. FIG.
13
and
FIG. 14
explain the prior separate dual volume system,
FIG. 15
explains the prior log structured file system, and
FIG. 16
explains the prior concurrent copy system.
The following methods are known as methods for copying logical-disk data in a prior RAID device.
(1) Separate Dual Volume System
In a system comprising a host
90
and RAID device
91
as shown in
FIG. 13
, first a copy instruction is sent from the host
91
, as shown in
FIG. 14
, and the copy-source volume (logical disk)
93
is prepared (defined). Next, in response to an “Establish Pair” instruction, copying begins from a primary (copy-source logical disk)
93
to a secondary (copy-destination logical disk)
94
(create a dual state). Establishment of a pair is completed after copying is finished (after the dual state is created). After this dual state is created, an update process request from the host
90
is reflected by primary (copy-source logical disk)
93
and secondary (copy-destination logical disk)
94
. By issuing an instruction to separate the dual pairs, copying of the logical volume at this state is complete. Now, as shown in
FIG. 13
, it is possible for different hosts (applications)
90
,
95
to use the primary (copy-source logical disk)
93
and secondary (copy-destination logical disk)
94
.
As shown in
FIG. 14
, the primary (copy-source logical disk)
93
can be accessed during copying, however, the secondary (copy-destination logical disk) cannot be accessed during copying.
(2) Log Structured File System
As shown in
FIG. 15
, logical disks A, B, C have been defined by the host. Each data block is stored in one physical disk
96
. Each of the logical disks is defined by a data pointer of the physical disk
96
. Copying from a logical disk A to a logical disk B, is performed by setting the pointer of the logical disk B as pointer of the logical disk A.
Moreover, the update data B
2
for the logical disk B are stored in the physical disk separately from the original data. Also, by updating the pointer of the logical disk B to the pointer of the update data B
2
, it is possible to update the logical disk B without changing the original data A
1
to A
6
of the logical disk A.
This method is not followed by copying of actual data, and by setting pointers, the copy operation can completed immediately.
(3) Concurrent Copy System
As shown in
FIG. 16
, when copying from the copy-source disk
93
to the copy-destination disk
94
, the host
90
reads the data to be copied from the copy-source disk (A), and with a data transfer function, writes the data to the copy-destination disk
94
. The bitmap of the copied address is set as copied.
When there is an update request for an uncopied area of the copy-source disk
93
during copying, that data of the copy-source disk
93
is stored away in a side file
92
as shown a mark (
1
). That address portion of the bitmap is set as being stored away in a side file as shown a mark (
2
). The copy-source disk
93
is also updated as shown a mark (
3
). When copying data that have been stored away in the side file
92
, the data to be copied are read from the side file
92
and, with the data transfer function, are written to the copy-destination disk
94
as shown a mark (
4
). This method makes it possible for the host to reference and update the copy-source disk
93
during copying.
The prior art, however, had the following problems.
(1) In the separate dual volume system shown in FIG.
13
and
FIG. 14
, it is not possible to access the copy-source disk during copying. Therefore, to access the copy-source disk it is necessary to wait until copying is finished. For example, copying 9 Gbytes takes about 1 hour, so it is necessary to wait 1 hour. Therefore operation must be performed on a schedule.
(2) In the log structured system shown in
FIG. 15
, it is possible to access both the copy-source logical disk and copy-destination logical disk with a copy instruction, however, since actual data are not copied, the advantages of a dual system where data are copied on separate disks cannot be realized. In other words, damage to the copy-source logical disk is also damage to the copy-destination logical disk, so when the copy-destination physical disk is damaged, it is also not possible to use the copy-source logical disk. Moreover, accessing the copy-destination physical disk, also means accessing the copy-source physical disk, so it is not possible to obtain high-speed performance from using separate disks.
(3) In the concurrent copy system shown in
FIG. 16
, access of the copy-source logical disk is also possible during copying, however, in order to access the copy-destination logical disk, it is necessary to wait unit copying is finished.
SUMMARY OF THE INVENTION
The objective of this invention is to provide a logical-disk copying method, disk-storage system and storage medium that can be accessed immediately in the copy complete state according to a copy instruction even though copying real data.
Another objective of this invention is to provide a logical-disk copying method, disk-storage system and storage medium for making it possible to access a copy-destination logical disk even during copying.
A further objective of this invention is to provide a logical-disk copying method, disk-storage system and storage medium for determining whether or not the access area has been copied and for making it possible to access the copy-destination logical disk.
This invention is a method for copying data from a copy-source logical disk to a copy-destination logical disk according to a copy instruction. This copying method comprises a step of copying data, in units of each area divided the copy-source logical disk, from the copy-source logical disk to the copy-destination logical disk, a step of interrupting the copy process when receive an access request for the copy-source logical disk or the copy-destination logical disk during copying, and a step of processing said access request.
This access processing step comprises a step of updating the target access area of the copy-source logical disk after the
Kaiya Norikazu
Kato Tadaomi
Onda Yasuhiro
Dinh Ngoc
Fujitsu Limited
Gossage Glenn
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