3
How MirrorView Handles Failures
3-5
About MirrorView Remote Mirroring Software
resources at both sites while maintaining duplicate copies of all data
at both sites.

Integration with EMC SnapView LUN Copy Software

EMC SnapView so ftware allow s users to cre ate a snaps hot copy of a n
active LUN at any point in time. The snapshot copy is a consistent
image that can serve for backup while I/O continues to the original
LUN. You can use SnapView in conjunction with MirrorView to make
a backup copy at a remote site.
A common situation for disaster recovery is to have a primary and a
secondary site that are geographically separate. MirrorView ensures
that the data from the primary site replicates to the secondary site.
The secondary site sits idle until there is a failure of the primary site.
With the addition of SnapView at the secondary site, the secondary
site can take snapshot copies of the replicated images and back them
up to other media, providing time-of-day snapshots of data on the
production host with minimal overhead.
How MirrorView Handles Failures
When a failure occurs during normal operations, MirrorView
implements several actions to recover.

Primary Image Failure

When the server or storage system running the primary image fails,
access to the mirror stops until a secondary is promoted to primary or
until the primary is repaired. If promotion occurred, then the primary
was demoted to secondary and it must be synchronized before
rejoining the mirror. If the primary was repaired, then the mirror
continues as before the failure.
For fast synchronization of the images after a primary failure,
MirrorView provides a write-intent log feature. The write intent log
records the current activity so that a repaired primary need only copy
over data that recently changed (instead of the entire image), thus
greatly reducing the recovery time.