Snapshot management
- What a Snapshot copy is
A Snapshot copy is a frozen, read-only image of a traditional volume, a FlexVol volume, or an aggregate that captures the state of the file system at a point in time.
- About user access to Snapshot copies
By default, every volume contains a directory named .snapshot, through which users can access old versions of files in that directory. Users can gain access to Snapshot copies depending on the file-sharing protocol used—NFS or CIFS. Access to Snapshot copies can be turned off.
- How Data ONTAP Snapshot copies work in an iSCSI or FCP network
Snapshots of applications running on a file system might cause the Snapshot copy to have inconsistent data unless measures are taken (such as, quiescing the application prior to taking the Snapshot copy) to ensure that the data on disk is logically consistent before you take the Snapshot copy.
- Restoring files from Snapshot copies
You might need to restore a file from a Snapshot copy if the file was accidentally erased or corrupted. If you have purchased the SnapRestore option, you can automatically restore files or volumes from Snapshot copies with one command.
- Creating Snapshot schedules
Data ONTAP provides a default Snapshot schedule for each volume. You can configure the schedule to fit your needs.
- Creating Snapshot copies
The snap sched command automatically creates Snapshot copies at preset intervals in a Snapshot schedule. You can also create Snapshot copies manually at any time.
- Why you need to access a particular Snapshot copy
You might need to access a particular Snapshot copy (a version of a file at a particular point in time) because a file was changed, corrupted, or erased and the problem was not noticed until after one or more Snapshot copies of it were created. When you start looking for the version of the file you need, you will look for it by means of the access time of the Snapshot copy.
- What Snapshot disk consumption is
Data ONTAP preserves pointers to all the disk blocks currently in use at the time the Snapshot copy is created. When a file is changed, the Snapshot copy still points to the disk blocks where the file existed before it was modified, and changes are written to new disk blocks.
- What file folding means and how it saves disk space
File folding describes the process of checking the data in the most recent Snapshot copy, and, if it is identical to the Snapshot copy currently being created, just referencing the previous Snapshot copy instead of taking up disk space writing the same data in the new Snapshot copy.
- Displaying the rate of change of data, between two Snapshot copies
You can see the rate of change between two successive Snapshot copies in a volume. Data ONTAP displays the rates of change between successive Snapshot copies in a volume.
- Deleting Snapshot copies automatically
You can define and enable a policy for automatically deleting Snapshot copies.
- Displaying space reclaimed from deleted Snapshot copies
You can display the amount of space you can reclaim by deleting one or more Snapshot copies in a volume. The amount of space displayed is an approximation because writing to the volume, creating Snapshot copies, or deleting Snapshot copies cause the reclaimed amount to change.
- How to determine which Snapshot copies to delete on the basis of size
You must first list the Snapshot copies to determine which Snapshot copy to delete to free the most disk space.
- Renaming Snapshot copies
You might want to rename a Snapshot copy generated by the snap sched command if it contains data that you want to save (the snap sched command overwrites and deletes regularly scheduled Snapshot copies). You can use the snap rename command to save a Snapshot copy that contains data you want.
