VERITAS Volume Manager 3.1 Administrator's Guide

Volume Manager Operations
FastResync (Fast Mirror Resynchronization)
Chapter 3 115
Resynchronization), and the second is to extend the snapshot model
(Fast Mirror Reconnect) to provide a method by which snapshots can
be refreshed and re-used rather than discarded.
Fast Mirror Resynchronization Component
The former enhancement, Fast Mirror Resynchronization (FMR),
requires keeping track of data store updates missed by mirrors that were
unavailable at the time the updates were applied. When a mirror returns
to service, it must re-apply only the updates missed by that mirror. With
FMR, this process requires an amount of restoration far less than the
current method whereby the entire data store is copied to the returning
mirror.
An unavailable mirror is one that has been detached from its volume
either automatically (by VxVM, as the result of an error), or directly by
an administrator (via a VxVM utility such as the vxplex or vxassist
commands). A returning mirror is a mirror that was previously
detached and is in the process of being re-attached to its original volume
as the result of the vxrecover or vxplex att operation.
FMR will not alter the current mirror failure and repair administrative
model. The only visible effect is that typical mirror repair operations
conclude expediently.
The resynchronization enhancement allows the administrator to
enable/disable FMR on a per-volume basis, and to check FMR status.
Fast Mirror Reconnect Component
Fast Mirror Reconnect augments the existing snapshot usage model.
Without Fast Mirror Resynchronization, an independent copy of a a
volume is created via the snapshot mechanism. The original volume and
the snap volume are completely independent of each other and, their
data may diverge.
The Fast Mirror Reconnect snapshot enhancement makes it possible
to re-associate a snapshot volume with its original peer for the express
purpose of reducing the work-load required to perform cyclic operations
which rely heavily upon the VxVM snapshot functionality.
FMR Enhancements to VxVM Snapshot Functionality
The FMR snapshot enhancements to Release 3.1 extend the snapshot
model as shown in Figure 3-1, FMR Enhanced Snapshot,. Beginning