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Dirty region logging

Dirty region logging (DRL), if enabled, speeds recovery of mirrored volumes after a system crash. DRL keeps track of the regions that have changed due to I/O writes to a mirrored volume. DRL uses this information to recover only those portions of the volume that need to be recovered.

If DRL is not used and a system failure occurs, all mirrors of the volumes must be restored to a consistent state. Restoration is done by copying the full contents of the volume between its mirrors. This process can be lengthy and I/O intensive. It may also be necessary to recover the areas of volumes that are already consistent.

  Note   DRL adds a small I/O overhead for most write access patterns.

If a version 20 DCO volume is associated with a volume, a portion of the DCO volume can be used to store the DRL log. There is no need to create a separate DRL log for a volume which has a version 20 DCO volume.

See "DCO volume versioning" on page 68.