Snapshotting Shadow File Systems
Snapshotting Shadow File Systems
Shadow filesystems can be snapshotted; however, the state of what is included in the snapshot
is arbitrary. Files that have not yet been migrated will not be present, and implementation
details (such as SUNWshadow extended attributes) may be visible in the snapshot. This
snapshot can be used to restore individual files that have been migrated or modified since
the original migration began. Because of this, it is recommended that any snapshots be kept
on the source until the migration is completed, so that unmigrated files can still be retrieved
from the source if necessary. Depending on the retention policy, it may be necessary to extend
retention on the source in order to meet service requirements. While snapshots can be taken,
these snapshots cannot be rolled back to, nor can they be the source of a clone.
Backing Up Shadow File Systems
Filesystems that are actively migrating shadow data can be backed using NDMP as with any
other filesystem. The shadow setting is preserved with the backup stream, but will be restored
only if a complete restore of the filesystem is done and the share doesn't already exist. Restoring
individual files from such a backup stream or restoring into existing filesystems may result
in inconsistent state or data corruption. During the full filesystem restore, the filesystem will
be in an inconsistent state (beyond the normal inconsistency of a partial restore) and shadow
migration will not be active. Only when the restore is completed is the shadow setting restored.
If the shadow source is no longer present or has moved, the administrator can observe any
errors and correct them as necessary.
Replicating Shadow File Systems
Filesystems that are actively migrating shadow data can be replicated using the normal
mechanism, but only the migrated data is sent in the data stream. As such, the remote side
contains only partial data that may represent an inconsistent state. The shadow setting is sent
along with the replication stream, so when the remote target is failed over, it will keep the same
shadow setting. As with restoring an NDMP backup stream, this setting may be incorrect in
the context of the remote target. After failing over the target, the administrator can observe any
errors and correct the shadow setting as necessary for the new environment.
Shadow Migration 433
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