Snapshots

Snapshots are a implementation of copy-on-write that allows for a file system to quickly take a point-in-time copy of the file system and provide access to the data through a .snapshot directory. Snapshots provide a fast, user-accessible way to recover data that has been accidentally deleted or corrupted within a recent time window -- rather than having to retrieve the data from comparatively slow tape backups. They also help to span the time gap between full backups.

We provide Snapshots on our ZFS and FluidFS filers to certain file systems. If you are ever unsure if a particular volume has Snapshots enabled, please contact the Help Desk.

Snapshot Policy

Our core file systems in the department are on a 4 hour snapshot cycle. Snapshots are taken at,

12am

4am

8am

12pm

4pm

8pm

We retain up to 8 hourly snapshots, 2 daily snapshots and 1 weekly snapshot.

Snapshot Restoring

If you have deleted a file by mistake and you need to get it back, you can use the snapshots directory to recopy the file.

This directory can typically be found in your home directory. It will be either:

• .snapshots for the FluidFS filer
• .zfs/snapshot for the ZFS filer

The inside of one of these will look something like this on a FluidFS filesystem:

sattwood@zaphod:~$ pwd
/nfshomes/sattwood
sattwood@zaphod:~$ cd .snapshots
sattwood@zaphod:~/.snapshots$ ls
daily_2018_06_13__00_00  hourly_2018_06_14__04_00  hourly_2018_06_14__16_00  hourly_2018_06_15__08_00
daily_2018_06_14__00_00  hourly_2018_06_14__08_00  hourly_2018_06_14__20_00  hourly_2018_06_15__12_00
daily_2018_06_15__00_00  hourly_2018_06_14__12_00  hourly_2018_06_15__04_00  weekly_2018_06_09__00_00

Or this, on a ZFS filesystem:

sattwood@swirl:~$ pwd
/nmhomes/sattwood
sattwood@swirl:~$ cd .zfs/snapshot
sattwood@swirl:~/.zfs/snapshot$ ls
zfs-auto-snap_daily-2018-06-13-01h00   zfs-auto-snap_hourly-2018-05-28-00h00
zfs-auto-snap_daily-2018-06-14-01h00   zfs-auto-snap_hourly-2018-05-29-00h00
zfs-auto-snap_daily-2018-06-15-01h00   zfs-auto-snap_hourly-2018-06-03-16h00
zfs-auto-snap_hourly-2018-05-24-00h00  zfs-auto-snap_hourly-2018-06-10-08h00
zfs-auto-snap_hourly-2018-05-25-00h00  zfs-auto-snap_hourly-2018-06-15-12h00
zfs-auto-snap_hourly-2018-05-26-00h00  zfs-auto-snap_weekly-2018-06-09-03h00

For an example of file restoration, please see this page.