I've moved 700GB off, drive space not freed?

[diskdiddler]

Any ideas? My NAS is very very high in space, so I said, right, time to clear it.

Moved 700GB off it, no sign of the data where it was. Space didn't free, even after 45 minutes.
Rebooted it, still no sign of the space.

(No, it's not in the recycle bin)

Latest stable (11.4?) I'll assume it's not a bug and just some oddity has gone on?

 

[MrToddsFriends]

Snapshots?

 

[diskdiddler]

Snapshots?

Hmmm! I... I think that IS the drive I keep snap shots of, yes.

So in 3 days it will come back right.

 

[diskdiddler]

Yep it's that! Phew thanks.


So just to clarify, because of the way the snap shot system is designed, I have a snap shot per day, lasts 3 days.


The change are all incremental right? The 700gb won't get re allocated back on to storage again will it? If another 700gb was suddenly used, I'd end up out of space and likely with a crashed system.

 

[sretalla]

Snapshots are incremental on top of the file system that's in place... of you have 700GB free and you add (or change) 700GB of files, you're toast.

When snapshots are deleted, they merge with the "current" snapshot (i.e. the actual/live filesystem) and free any space that is no longer pointed to in order to keep the integrity of that point in time, so you don't need to keep all snapshots in between the creation of the dataset and the last snapshot to ensure you can restore a snapshot and you can get back any space freed in between the snapshot and current time.

 

[MrToddsFriends]

So just to clarify, because of the way the snap shot system is designed, I have a snap shot per day, lasts 3 days.

The lifetime of snapshots and the interval between them is how you did set them up, not due to the design of ZFS snapshots.
http://doc.freenas.org/11/storage.html#periodic-snapshot-tasks

The 700gb won't get re allocated back on to storage again will it? If another 700gb was suddenly used, I'd end up out of space and likely with a crashed system.

Think of snapshots as of reference counters. After the last snapshot that references a specific data item is expired (or deleted) this reference counter has the value 0 and as a result the space in question is freed.

About deleting (or "destroying") snapshots:
http://doc.freenas.org/11/storage.html#snapshots

To avoid overfilling a pool I set up a "reservation" dataset only for this purpose with "reserved space for this dataset" set to a nonzero value (refers to the REFRESERVATION ZFS property).

 

[diskdiddler]

Thanks for the replies all, I'm glad I set up snapshots, very useful. Just kinda worried me on this one.

I'm gonna guess in about 3 days, suddenly 700GB should appear.