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 copy 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 system reboots with configuration files that were in effect when the Snapshot copy 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 copy 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 copy 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 copy 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 copy from a previous release of Data ONTAP. However, doing so can cause problems because of potential version incompatibilities and can prevent the system from booting completely.

Prerequisites

You must meet these prerequisites before using SnapRestore:

SnapRestore must be licensed on your storage system.
There must be at least one Snapshot copy on the system that you can select to revert.
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 copy, you cannot undo the reversion.
If you revert to a Snapshot copy taken before a SnapMirror Snapshot copy, Data ONTAP can no longer perform an incremental update of the mirror; it must re-create the baseline version of the mirror.
Snapshot copy deletions are irrevocable. If you delete a Snapshot copy, you cannot recover the Snapshot copy by using SnapRestore.
After you revert a volume to a selected Snapshot copy, you lose all the Snapshot copies that were taken after the selected Snapshot copy.
Between the time you enter the snap restore command and the time when reversion is completed, Data ONTAP stops deleting and creating Snapshot copies.
If you are reverting a file from a Snapshot copy, you can delete other Snapshot copies, except for the Snapshot copy you are reverting from.

Caution about reverting the root volume

Because the /etc directory of the root volume contains configuration information about the system, reverting the root volume might change the configuration. In addition, restoring the root volume restores options settings for the entire system to the settings that were in effect when the Snapshot copy 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 storage system before using SnapRestore. After you revert the root volume, restore the /etc directory and reboot. If you back up the /etc directory to another volume, you can use the following command to make the system reboot with that volume as the root volume: vol options volume root In this way, when the system reboots during a revert, 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 storage system before using SnapRestore. After you revert the root volume, restore the /etc directory and reboot.

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

vol options volume root

In this way, when the system reboots during a revert, it can use the correct settings in the /etc directory.