Snapshot Technique for Shared Large Storage in San Environments

Y.H. Kim, C.S. Kim, D.J. Kang, Y. Bak, and M.-J. Kim (Korea)


Snapshot, Shared Storage, SAN (Storage Area Network)


Recent Enterprise system for web servers, GIS servers and e-commerce demands online backup capability to protect data that must be available continuously and eliminate the down-time needed to perform traditional off line backup. Snapshots allow applications and users to take online backup only needed a few seconds delay during snapshot initiation. However, traditional snapshot technique has some limits adapted to large amount storage shared by multi-hosts in the following aspects. As volume size grows, (1) it deteriorates crucially the performance of write operations due to additional disk access to verify COW is performed. (2) Also it increases excessively the blocking time of write operation performed during the snapshot creation time. In this paper, we propose an efficient snapshot technique for large amount storage shared by multi-hosts in SAN Environments. We eliminate the blocking time of write operation caused by freezing while a snapshot creation is performing. Also to improve the performance of write operation when snapshot is taken, we introduce First Allocation Bit(FAB) and Snapshot Status Bit(SSB). It improves performance of write operation by reducing an additional disk access to volume disk for getting snapshot mapping block.

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