Snapshot Size For ZFS Volume

[BobCochran]

I have an approximately 11 Tb ZFS volume which is 60% full. I've never taken a snapshot of it. If I take a snapshot, won't this be a copy of my actual data (6.2T) and will therefore exceed the size of the volume?

Or can I have the snapshot stored on a different host system?

Thanks

Bob

 

[Stephens]

http://docs.oracle.com/cd/E19963-01/html/821-1448/gbciq.html

 

[JaimieV]

Snapshots are not backups, they're a marker of "the data at that moment". Once you've made one snapshot, any changes to the snapshotted content will increment the amount of data on the disk, eg if you change a file then the new version is added to the total instead of replacing the original.

So the first snapshot uses negligable extra space. Further snapshots use space that matches the amount of data changed (added and modified) since the previous snapshot.

If by saying "I've never taken a snapshot of it" you actually mean "This data is not backed up anywhere else", then that's a different thing and you should sort out a backup sharpish!

 

[BobCochran]

Stephens and JaimieV, thanks for your help! I don't have a backup system set up for this yet, that is why I am asking about snapshots. I'm thinking of either buying an SAS expander, adding this to the existing NAS, then adding hard drives meant for backup capacity, and rsyncing the ZFS datasets to the new disks. If I can do this it seems less costly than setting up a second system. That is also an alternative -- I can set up a second system and then either rsync my data to that other system or replicate ZFS snapshots to the other system. I agree I better sort out a backup!

Bob