Dell EMC Metro node 7.0.1 Administrator Guide

There are two types of rebuild behavior:

• A full rebuild copies the entire contents of the source to the target.
• A logging rebuild copies only changed blocks from the source to the target.

Local mirrors are updated using a full rebuild (local devices do not use logging volumes).

In metro node Metro configurations, all distributed devices have an associated logging volume. Logging volumes keep track of blocks that are written during an inter-cluster link outage. After a link or leg is restored, the metro node system uses the information in logging volumes to synchronize mirrors by sending only changed blocks across the link.

Logging volume rebuilds also occur when a leg of a distributed RAID 1 becomes unreachable, but recovers quickly.

If a logging volume is unavailable at the time that a leg is scheduled to be marked out-of-date, the leg is marked as fully out-of-date, causing a full rebuild.

The unavailability of a logging volume matters both at the time of recovery (when the system reads the logging volume) and at the time that a write fails on one leg and succeeds on another (when the system begins writes to the logging volume).

See Logging volumes.