Electrical computers and digital processing systems: memory – Storage accessing and control – Control technique
Reexamination Certificate
1999-06-04
2001-01-30
Chan, Eddie P. (Department: 2751)
Electrical computers and digital processing systems: memory
Storage accessing and control
Control technique
C711S114000, C711S113000, C711S112000, C714S006130, C707S793000
Reexamination Certificate
active
06182198
ABSTRACT:
The present invention relates generally to various method for implementing improved backup procedures for disk arrays, and particularly for implementation on the DAC9060SX and DAC9060SF disk array controllers.
TECHNICAL FIELD
Background of the Invention
The problem of data backup continues to grow with the storage capacity of disk drive arrays. Disk drives continue to grow in speed and capacity, while cost per unit storage continues to decline. This explosion of capacity has placed severe demands on data backup techniques. RAID mechanisms have the potential to minimize the frequency of backups.
As servers become increasingly fault tolerant, RAID storage systems are expected to remain available at all times. Backup procedures can be performed directly by the host system, but this results in lowered system performance. In addition, there are issues with on-line data base systems where a consistent copy of the database is required not only for backup, but for data mining operations. In these cases, the backup copy of the array can be made while normal read and write operations continue to the storage system. This is referred to as a snapshot.
In the prior art, a snapshot backup is accomplished using RAID
1
or mirrored disk drives in a storage system, as shown in FIG.
1
. The database is first synchronized to the storage system
21
to flush any data or meta-data out of the server's internal cache (not shown). The mirrored RAID set
22
b
is then removed, and placed into a second system
23
for backup or analysis. When complete, the mirrored set
22
b
is returned to the original storage system
21
where mirror set
22
b
is synchronized to a master set
24
. These systems usually use two mirrored drives
22
a,
22
b
to allow redundancy while one of the mirror sets
22
b
is used for backup.
There are several problems with this process:
The backup is a manual process. Human intervention is required to move the disks from one system to the next. This requires scheduling for the backup or checkpoint operation, as well as the cost of the operator. Physically moving the drives can also result in accidental damage to the drives through rough handling, and wear and tear on the connectors.
For a fully redundant system as shown in
FIG. 1
, a 200% storage overhead is required. These costs can include the disk drives, cooling fans, power supplies, UPS systems, cabinets, and floor space.
Performance degradation occurs on RAID subsystem
26
as replaced drives
22
a,
22
b
are rebuilt and made coherent with the master set
24
.
A restriction that applies to RAID subsystem
26
is that no knowledge of the file system can be assumed, and there is no a priori knowledge of read or write patterns. For any backup strategy other than host backup, there is no way to guarantee that the information on the drive is synchronized with the host system. A method for synchronizing the host cache to the storage system is always be required.
Therefore it would be desirable to provide a new and improved method and apparatus for generating a snapshot backup that is capable of dealing with arbitrarily large disk arrays, and utilizes a smaller storage overhead.
It would also be desirable to provide a new and improved method and apparatus for generating a snapshot backup that can allow read and write operations to occur while a snapshot backup is in progress.
It would also be desirable to provide a new and improved method and apparatus for generating a snapshot backup that can implement the use of dual-active controllers.
SUMMARY OF THE INVENTION
The present invention is a method and system of performing a snapshot backup of a storage unit of a host system. The host system includes at least one primary system drive, a primary logic unit, a log system drive and at least one backup logic unit. A particular method is designed to perform the snapshot backup while allowing normal read operations and write operations to occur. After initializing the snapshot backup, the method processes a write operation of new data submitted to the primary logic unit to be written to a sector of the primary system drive during the snapshot backup by reading the old data that is on the primary system drive which is to be overwritten by the new data in response to the write operation, buffering the old data, overwriting the old data with the new data and writing the old data to the log system drive if the write operation is the first write operation to that specific sector in the primary system drive for the snapshot backup. The method executes a read operation during the snapshot backup by processing the read operation submitted to the backup logic unit by accessing the requested data of the read operation from the log system drive if the requested data is available from the log system drive and returning the requested data to a requester, if not, accessing the requested data from the primary system drive and returning the requested data to the requester.
A particular system embodiment implemented in a host system performs a snapshot backup of the drive system of the host system. The system includes at least one controller which initializes and terminates the snapshot backup. The system further includes at least one backup logic unit which is electronically coupled to a log system drive such that the requested data is accessed from the log system drive if the requested data is available from the log system drive during a read operation and is returned to the requester. If the data is not available from the log system drive then the backup logic unit, which is also electronically coupled to at least one primary system drive, accesses the requested data from the primary system drive during the read operation and returns the data to the requester. The system further includes at least one primary logic unit which is electronically coupled to the primary system drive such that new data submitted to the primary logic unit during a write operation is written to a sector of the primary system drive. A buffer is electronically coupled to the primary system drive such that the old data that is to be overwritten by the new data submitted to the primary logic unit is buffered prior to being overwritten. The buffer is further electronically coupled to the log system drive such that the old data is written to the log system drive if the new data written to the primary system drive is the first data to be written to the sector during the snapshot backup.
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User's Guide Novell Perfect Office for Windows, Word Perfect, The Best-Selling Word Processor for all Time v 6.1, pp 152-154, 159, & 753-754, 1994.
Hubis Walter A.
Otterness Noel S.
Chan Eddie P.
Flehr Hohbach Test Albritton & Herbert LLP
International Business Machines - Corporation
Kim Hong
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