HP StorageWorks Storage Mirroring user's guide (T2558-96073, February 2008)

14 - 20
To be completely assured that your data on the target is good, automatic and scheduled snapshots only occur when the data
is in a good Storage Mirroring state. However, manual snapshots can be taken during any state. There are instances when you
may want to take a manual snapshot, even if the target data is in a bad state. For example, if you drop an operation, that does
not necessarily mean your data on the target is corrupt or the target would be unable to stand in for the source in the event
of a failure. A snapshot of a bad state may be useful and usable, depending on your environment. If your source is a file server
and an operation has been dropped, it is just one user file that is out-of-date. All of the remaining target files are intact and
can be accessed in the event of a failure. However, if your source is an application server and an operation has been dropped,
that one file could cause the application not to start on the target in the event of a failure. In these cases, manual snapshots
of a bad state depend on the context of your environment.
If you are using the Management Console, check the
Target Data State column to see the current state of the data on the
target. If you are using the Text Client, use the
status target Storage Mirroring DTCL command to determine the state
of the data on the target.
Restore
Required
Good
or Bad
The data on the target no
longer matches the data on the
source because of a failover.
This does not necessarily mean
that the data on the target is
bad.
Scheduled and automatic
snapshots will be delayed until
a restore is completed or the
Restore Required state is
overruled by a mirror. Once
the restoration or mirror is
complete, automatic and
scheduled snapshots will occur
normally.
Restore the target data back to
the source or overrule the
Restore Required state by
performing a mirror. Once the
restoration or mirror is
complete, manual snapshots
can be taken normally.
Snapshot
Reverted
Good
or Bad
The data on the target no
longer matches the data on the
source because a snapshot has
been applied on the target.
This does not necessarily mean
that the data on the target is
bad.
Scheduled and automatic
snapshots will be delayed until
a restore is completed or the
Snapshot Reverted state is
overruled by a mirror. Once
the restoration or mirror is
complete, automatic and
scheduled snapshots will occur
normally.
Restore the target data back to
the source or overrule the
Snapshot Reverted state by
performing a mirror. Once the
restoration or mirror is
complete, manual snapshots
can be taken normally.
Restore
Complete
Good Because the restoration is
complete, the data on the
source and target is
synchronized.
Scheduled and automatic
snapshots will occur normally.
Manual snapshots can be taken
normally.
NOTE: Because the driver for Volume Shadow Copy is started before the driver for Storage Mirroring, if you revert
any files on the source that are contained in your replication set, Storage Mirroring will not be aware of the
revert and, therefore, the file change will not be replicated to the target. The file change will be mirrored to
the target during the next mirroring process.
Action State Description
Automatic Action
Taken for Scheduled
and Automatic
Snapshots
User Interaction
Required for Manual
Snapshots