Electrical computers and digital processing systems: memory – Storage accessing and control – Control technique
Reexamination Certificate
1998-04-17
2001-01-09
Thai, Tuan V. (Department: 2752)
Electrical computers and digital processing systems: memory
Storage accessing and control
Control technique
C711S154000, C711S161000, C711S165000
Reexamination Certificate
active
06173377
ABSTRACT:
AUTHORIZATION PURSUANT TO 37 C.F.R § 1.17(E)
A portion of the disclosure of this patent document contains command formats and other computer language listings all of which are subject to copyright protection. The copyright owner, EMC Corporation, has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.
FIELD OF THE INVENTION
This invention relates to data storage, and more particularly, to a system and method for automatically providing and maintaining a copy or mirror of data stored at a location geographically remote from the main or primary data storage device.
BACKGROUND OF THE INVENTION
Nearly all data processing system users are concerned with maintaining back-up data in order to insure continued data processing operations should their data become lost, damaged, or otherwise unavailable.
Large institutional users of data processing systems which maintain large volumes of data such as banks, insurance companies, and stock market traders must and do take tremendous steps to insure back up data availability in case of a major disaster. These institutions recently have developed a heightened awareness of the importance of data recovery and back-up in view of the many natural disasters and other world events including the bombing of the World Trade Center in New York City.
Currently, data processing system users often maintain copies of their valuable data on site on either removable storage media, or in a secondary “mirrored” storage device located on or within the same physical confines of the main storage device. Should a disaster such as fire, flood, or inaccessibility to a building occur, however, both the primary as well as the secondary or backed up data will be unavailable to the user. Accordingly, more data processing system users are requiring the remote storage of back up data.
One prior art approach at data back-up involves taking the processor out of service while back-up tapes are made. These tapes are then carried off premises for storage purposes. Should access to the backed up data be required, the proper tape must be located, loaded onto a tape drive, and restored to the host system requiring access to the data. This process is very time consuming and cost intensive, both in maintaining an accurate catalog of the data stored on each individual tape, as well as storing the large number of tapes required to store the large amounts of data required by these institutions. Additionally and most importantly, it often takes twenty-four hours before a back-up tape reaches its storage destination during which time the back-up data is unavailable to the user.
Additionally, today's systems require a significant amount of planning and testing in order to design a data recovery procedure and assign data recovery responsibilities. Typically, a disaster recovery team must travel to the test site carrying a large number of data tapes. The team then loads the data onto disks, makes the required network connections, and then restores the data to the “test” point of failure so processing can begin. Such testing may take days or even weeks and always involves significant human resources in a disaster recovery center or back-up site.
Some providers of prior art data storage systems have proposed a method of data mirroring whereby one host Central Processing Unit (CPU) or processor writes data to both a primary, as well as a secondary, data storage device or system. Such a proposed method, however, overly burdens the host CPU with the task of writing the data to a secondary storage system and thus dramatically impacts and reduces system performance.
Accordingly, what is required is a data processing system which automatically and asynchronously, with respect to a first host system, generates and maintains a back-up or “mirrored” copy of a primary storage device at a location physically remote from the primary storage device, without intervention from the host which seriously degrades the performance of the data transfer link between the primary host computer and the primary storage device.
SUMMARY OF THE INVENTION
This invention features a system which controls storing of primary data received from a primary host computer on a primary data storage system, and additionally controls the copying of the primary data to a secondary data storage system controller which forms part of a secondary data storage system, for providing a back-up copy of the primary data on the secondary data storage system which is located in a geographically remote location from the primary data storage system. For remote copying of data from one storage system to the other without host involvement, the primary and secondary data storage system controllers are coupled via at least one high speed communication link such as a fiber optic link driven by LED's or laser. The high speed communication link also permits one data storage system to read or write data to or from the other data storage system.
At least one of the primary and secondary data storage system controllers coordinates the copying of primary data to the secondary data storage system and at least one of the primary and secondary data storage system controllers maintains at least a list of primary data which is to be copied to the secondary data storage device.
Additionally, the secondary data storage system controller provides an indication or acknowledgement to the primary data storage system controller that the primary data to be copied to the secondary data storage system in identical form as secondary data has been received or, in another embodiment, has actually been written to a secondary data storage device.
Accordingly, data may be transferred between the primary and secondary data storage system controllers synchronously, when a primary host computer requests writing of data to a primary data storage device, or asynchronously with the primary host computer requesting the writing of data to the primary data storage system, in which case the remote data copying or mirroring is completely independent of and transparent to the host computer system.
At least one of the primary data storage system controller and the secondary data storage system controller maintains a list of primary data which is to be written to the secondary data storage system. Once the primary data has been at least received or optionally stored on the secondary data storage system, the secondary data storage system controller provides an indication or acknowledgement of receipt or completed write operation to the primary data storage system.
At such time, the primary and/or secondary data storage system controller maintaining the list of primary data to be copied updates this list to reflect that the given primary data has been received by and/or copied to the secondary data storage system. The primary or secondary data storage system controllers and/or the primary and secondary data storage devices may also maintain additional lists for use in concluding which individual storage locations, such as tracks on a disk drive, are invalid on any given data storage device, which data storage locations are pending a format operation, which data storage device is ready to receive data, and whether or not any of the primary or secondary data storage devices are disabled for write operations.
In accordance with one aspect of the invention, the remote mirroring facility can operate in a specified one of a number of different remote mirroring operating modes for each volume. The operating modes include a synchronous mode, a semi-synchronous mode, an adaptive copy-write pending mode, and an adaptive copy-disk mode. The operating mode for each logical volume can be specified to best suit the purposes of the desired remote mirroring, the particular application using the volume, and the particular use of the data stored on the volume.
In the synchronous mode, data on the primary (R1) and secondary (R
Alterescu Bruno
Castel Daniel D. C
Ofek Yuval
Shklarsky Gadi G
Vishlitzky Natan
EMC Corporation
Howrey Simon Arnold & White , LLP
Thai Tuan V.
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