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Recovery of data using write request copies in delta queue
| Details |
Inventors: Ohran, Richard; Price, Dan; Johnson, Randall;
Assignee: EMC Corporation (Hopkinton, MA)
Primary Examiner: Nguyen; Hiep T.
Assistant Examiner:
Attorney, Agent or Firm: Workman Nydegger
Recovering mirrored data after the failure of a computer using write requests stored in a delta queue of an associated computer without transmitting all of the mirrored data. A write request at a primary computer is stored in a delay buffer. A copy of the write request is transmitted to a backup computer and stored in a delta queue. The backup computer executes the copy of the write request and transmits acknowledgement of the receipt of the write request to the primary computer. In response to the acknowledgement, the primary computer executes the write request stored in the delay buffer. The computers then exchange subsequent acknowledgements of the write request execution, enabling the computers to delete the write requests. If the primary computer fails, the primary computer recovers data by receiving only the copies of write requests that remain stored in the delta queue of the backup computer. |
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DETAILED DESCRIPTION In accordance with the present invention, a method and system are provided in which data from a primary computer system is mirrored in a secondary backup computer system.
This system maintains complete synchronization between the primary and backup memory devices even should the primary computer system fail after a write request was executed in the memory of the primary computer system, but before the request is fully transmitted to the backup computer system.
For each write request, a copy of the request is written into a delay buffer associated with the primary computer system, and a copy is transmitted to the backup computer system.
After the write request has been fully transmitted to the backup computer system, the backup computer system informs the primary computer system (e.
g.
, by sending an acknowledgement signal) that the request has been received at the backup computer system.
The write request in the delay buffer of the primary computer system is executed only after the primary computer system receives the acknowledgement signal indicating that the backup computer system also received a copy of the write request.
Thus, if the primary computer system fails before a copy of the write request is transmitted to the backup computer system, the primary computer system will not have executed the write request since the write request was left unexecuted in the delay buffer.
Therefore, synchronization is not lost between the primary and backup computer systems.
Another advantage of this invention is that complete remirroring (i.
e.
, recopying) of data from the backup computer system to the primary computer system is not needed when the primary computer system is brought back into operation after a failure.
Both the primary and backup computer systems have a memory queue to which a copy of the write request is forwarded.
When the primary computer system determines that the write request has been executed in the memory device of the backup computer system, the primary computer system deletes that request from its memory queue
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