Deciding when to use SnapRestore

Considerations before using SnapRestore

You must take into account the following considerations before deciding whether to use SnapRestore to revert a file or volume.

If the volume that you need to restore is a root volume, it is easier to copy the files from a snapshot or restore the files from tape than to use SnapRestore because you can avoid rebooting. If you need to restore a corrupted file on a root volume, however, a reboot is not necessary.
If you revert the whole root volume, the filer reboots with configuration files that were in effect when the snapshot was taken.
If the amount of data to be recovered is large, SnapRestore is the preferred method, because it takes a long time to copy large amounts of data from a snapshot or to restore from tape.
If a file to be recovered needs more space than the amount of free space in the active file system, you cannot restore the file by copying from the snapshot to the active file system. For example, if a 10-GB file is corrupted and only 5 GB of free space exists in the active file system, you cannot copy the file from a snapshot to recover the file. However, SnapRestore can quickly recover the file in these conditions. You do not have to spend time making the additional space available in the active file system.
Caution
SnapRestore lets you revert to a snapshot from a previous release of Data ONTAP. However, doing so can cause problems because of potential version incompatibilities and can prevent the filer from booting completely.

Prerequisites

You must meet these prerequisites before using SnapRestore:

SnapRestore must be licensed on your filer.
There must be at least one snapshot on your filer that you can select for the reversion.
The volume to be reverted must be online.
The volume to be reverted must not be a mirror used for data replication.

General cautions

Be sure that you understand the following facts before using SnapRestore:

SnapRestore overwrites all data in the file or volume. After you use SnapRestore to revert to a selected snapshot, you cannot undo the reversion.
If you revert to a snapshot taken before a SnapMirror snapshot, Data ONTAP can no longer perform an incremental update of the mirror; it must re-create the baseline version of the mirror.
Snapshot deletions are irrevocable. If you delete a snapshot, you cannot recover the snapshot by using SnapRestore.
After you revert a volume to a selected snapshot, you lose all the snapshots that were taken after the selected snapshot.
Between the time you enter the snap restore command and the time when reversion is completed, Data ONTAP stops deleting and creating snapshots.
If you are reverting a file from a snapshot, you can delete other snapshots, except for the snapshot you are reverting from.

Caution about reverting the root volume

Because the /etc directory of the root volume contains configuration information about the filer, reverting the root volume might change the filer configuration. In addition, restoring the root volume restores options settings for the entire filer to the settings that were in effect when the snapshot was taken. Reverting a root volume requires rebooting the system.

Preserving configuration files

To avoid reverting the configuration files, complete the following step.

Step	Action
1	Store all data that might need to be reverted in a volume other than the root volume. This ensures that you never need to revert the root volume.

Reverting a root volume

If you need to revert a root volume, complete the following step.

Step	Action
1	If the data you want to revert resides in the root volume, back up the /etc directory to another volume or another filer before using SnapRestore. After you revert the root volume, restore the /etc directory and reboot the filer. If you back up the /etc directory to another volume, you can use the following command to make the filer reboot with that volume as the root volume: vol options volume root In this way, when the filer reboots during the reversion, it can use the correct settings in the /etc directory.

Step

Action

If the data you want to revert resides in the root volume, back up the /etc directory to another volume or another filer before using SnapRestore. After you revert the root volume, restore the /etc directory and reboot the filer.

If you back up the /etc directory to another volume, you can use the following command to make the filer reboot with that volume as the root volume:

vol options volume root

In this way, when the filer reboots during the reversion, it can use the correct settings in the /etc directory.