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Data storage with host-initiated synchronization and fail-over of remote mirror
| Details |
Inventors: DeKoning, Rodney A.;
Assignee: LSI Logic Corporation (Milpitas, CA)
Primary Examiner: Iqbal; Nadeem
Assistant Examiner: Bonura; Timothy M.
Attorney, Agent or Firm: Suiter West PC LLO
A mirrored data storage system utilizes a first host device and a local storage device for primary data storage and a second host device and a remote storage device for mirrored, fail-over storage on behalf of client devices. At periodic intervals (called checkpoints), the first host device initiates data synchronization between itself and the two storage devices and issues checkpoint information to ensure that each device maintains information for a common stable storage state. The local storage device synchronizes its stored data and forwards the checkpoint information to the remote storage device. The remote storage device maintains a copy (called a snapshot) of the data at the common stable storage state. Given the snapshot and the checkpoint information, the remote storage device can restore itself to the common stable storage state in the event of a failure of the first host device and/or the local storage device. Upon failure of the first host device and/or the local storage device, the second host device is instructed to initiate a switch, or fail-over, to serving as the primary data storage on behalf of the client devices. |
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DETAILED DESCRIPTION The present invention enables efficient remote data mirroring and "fail-over" capabilities in a computer system wherein a local host device stores data on a local storage device on behalf of various client devices, and mirrors the data storage on a remote storage device.
"Fail-over" refers to a situation in which the local storage device can no longer service data access requests, so the client devices must switch to using remote storage device with a remote host device for data backup processing.
The local host device periodically initiates data synchronization procedures for the local and remote storage devices.
Information regarding the latest synchronization procedures is maintained within the local host, local storage and remote storage devices.
The synchronization information defines a common, known, coherent state of stored data for all of these devices.
The time at which a data synchronization occurs is called a "checkpoint," and the condition of the stored data at which the coherent state is defined is called the "checkpoint state.
" The remote storage device maintains a "snapshot" of the data at the latest checkpoint state.
The snapshot is essentially a copy of a portion of the data as the data existed at the last checkpoint state.
Changes to the stored data on the remote storage device are accepted after each previously occurring checkpoint, but the data that was present at the last checkpoint is transferred to and preserved in the snapshot, so it can be restored at a later time if necessary.
Since the remote storage device maintains information describing the checkpoint state, in the event of a fail-over condition, the remote host device quickly and easily "rolls back" the state of the data stored on the remote storage device to the last common checkpoint state.
The data is restored from the snapshot.
Applications executing on the client devices, thus, restart at the restored checkpoint state with a minimum of interruption.
These and other improvements are achieved by storing and synchronizing data between a host device, a primary storage device and a secondary storage device
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