Thursday, November 12, 2009

DRL - Veritas Volume Manager

DRL - Dirty Region Logging:

The method by which the VxVM monitors and logs modifications to a plex as a bitmap of changed regions. For a volumes with a new-style DCO volume, the DRL is maintained in the DCO (Data Change Object) volume.

How does it works?
DRL logically divides a volume into a set of consecutive regions and keeps
track of the regions to which
writes occur. A log is maintained that contains a status bit representing each
region of the volume. For any write operation to the volume, the regions being
written are marked dirty in the log before the data is written.

If a write causes a log region to become dirty when it was previously clean
the log is synchronously written to disk before the write operation can occur.
On system restart, VxVM recovers only those regions of the volume that are
marked as dirty in the dirty region log.

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