System and method for multi-destination merge in a storage area network
View Patent ↗A data storage system adapted to maintain redundant data storage sets at a destination location(s) is disclosed. The data storage system establishes a copy set comprising a source volume and a destination volume. Data written to a source volume is automatically copied to the destination volume. The data storage system maintains a data log that may be activated when the destination volume is inaccessible due to, for example, a malfunction in the destination storage system or in the communication link between the source system and the destination system. I/O commands and the data associated with those commands are written to the data log, and after a destination system becomes available the information in the data log is merged into the destination volume to conform the data in the destination volume to the data in the source volume. The data log competes for disk capacity with other volumes on the system, and log memory is allocated as needed. If multiple remote sites are provided, then the system permits to implements a merge fence to manage the process of merging data into multiple destinations.
1. A method for writing information in a data log to one or more destinations in a storage network, wherein the data log is generated by a source controller in response to a failure of one or more destinations in the storage network, and wherein each write I/O from a host computer is assigned a group sequence number that is stored with a data entry corresponding to the write I/O, the method comprising:
setting a merge fence to the lowest group sequence number of the destination databases;
writing entries from the data log, beginning at the merge fence, to each active destination and for which the lowest group sequence number is equal to the merge fence; and
incrementing the merge fence after each write.
2. The method of claim 1 , further comprising merging data from the data log with data previously stored in the destination storage system to return the data to a consistent state.
3. The method of claim 1 , wherein the host computer continues to write data from the host computer to the data log while information is written from the data log to the one or more destinations.
4. The method of claim 1 , wherein the data log comprises a storage set treated as a logical unit by the source controller.
5. The method of claim 1 , wherein data written from the data log is stored in cache memory in a source controller in transaction order.
6. The method of claim 1 , wherein entries from the data log are written by the source controller in synchronous mode.
7. The method of claim 1 , wherein data written by the source controller is written in asynchronous mode.
8. The method of claim 1 , wherein the merge fence is reset if a destination with a group sequence number lower than the current group sequence number comes online during the write process.
9. A computer program product embodied in a computer readable storage medium for use in connection with a processor for writing information in a data log to one or more destinations in a storage network, wherein the data log is generated by a source controller in response to a failure of one or more destinations in the storage network, and wherein each write I/O from a host computer is assigned a group sequence number that is stored with a data entry corresponding to the write I/O, comprising logic instructions stored in a computer-readable medium which, when executed by a processor, configure the processor to:
set a merge fence to the lowest group sequence number of the destinations;
write entries from the data log, beginning at the merge fence, to each active destination for which the lowest group sequence number is equal to the merge fence; and
increment the merge fence after each write.
10. The computer program product of claim 9 , further comprising logic instructions stored in a computer-readable medium which, when executed by a processor, configure the processor to process write data from the host computer written to the data log while data is written from data log to the one or more destinations.
11. The computer program product of claim 9 , further comprising logic instructions stored in a computer-readable medium which, when executed by a processor, configure the processor to reset the merge fence if a destination with a group sequence number lower than the current group sequence number comes online during the write process.
12. The computer program product of claim 11 , further comprising logic instructions stored in a computer-readable medium which, when executed by a processor, configure the processor to receive data written from the host computer while merging is being performed.