Difference between revisions of "Snapshots"

From UMIACS
Jump to navigation Jump to search
 
(16 intermediate revisions by 2 users not shown)
Line 1: Line 1:
Snapshots are a implementation of [http://en.wikipedia.org/wiki/Copy-on-write 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.
+
Snapshots are a implementation of [http://en.wikipedia.org/wiki/Copy-on-write 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 [[Snapshots:FluidFS | FluidFS]] filers to certain file systems. If you are ever unsure if a particular volume has Snapshots enabled, please contact the [[HelpDesk | Help Desk]].
+
We provide snapshots on our Isilon, ZFS, and FluidFS filers to certain file systems. If you are ever unsure if a particular volume has snapshots enabled, please contact the [[HelpDesk | Help Desk]].
  
==Snapshot Policy==
+
==Snapshot Retention Policy==
 +
Our core file systems in the department are on a 4 hour snapshot cycle. 
  
Our core file systems in the department are on a 4 hour snapshot cycle.  Snapshots are taken at,
+
{| class="wikitable"
 
+
!Snapshot Name
{| style="color:green; background-color:#ffffcc;" cellpadding="5" cellspacing="0"
+
!Retention Length
| 12am
+
!When is it taken?
| 4am
+
|-
| 8am
+
|'''Hourly'''
| 12pm
+
|24-32 hours
| 4pm
+
|Every day 12am, 4am, 8am, 12pm, 4pm
| 8pm
+
|-
 +
|'''Daily'''
 +
|2 days
 +
|Every day 8pm or 12am
 +
|-
 +
|'''Weekly'''
 +
|1 week
 +
|Every Saturday 8pm or Sunday 12am
 
|}
 
|}
  
We retain up to 8 hourly snapshots, 2 daily snapshots and 1 weekly snapshot.
+
In other words, we retain up to either 6 or 8 hourly snapshots, 2 daily snapshots and 1 weekly snapshot. Hourly snapshots may be superseded by daily snapshots, and daily snapshots may be superseded by the weekly snapshot.
  
 
==Snapshot Restoring==
 
==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.
 
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.
  
Line 25: Line 32:
  
 
'''It will be either''':
 
'''It will be either''':
 +
* .snapshot for the Isilon filer
 +
* .zfs/snapshot for the ZFS filer
 +
* .snapshots for the FluidFS filer
  
* .snapshots for the [[Snapshots:FluidFS | FluidFS]] filer
+
The inside of one of these will look like:
* .zfs/snapshot for the ZFS filer
 
  
The inside of one of these will look something like this on a FluidFS filesystem:
+
Isilon filesystem:
 
<pre>
 
<pre>
sattwood@zaphod:~$ pwd
+
sattwood@coffee:~$ pwd
 
/nfshomes/sattwood
 
/nfshomes/sattwood
sattwood@zaphod:~$ cd .snapshots
+
sattwood@coffee:~$ cd .snapshot
sattwood@zaphod:~/.snapshots$ ls
+
sattwood@coffee:~/.snapshot$ 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
+
nfshomes_2018-06-14_00:00 nfshomes_2018-06-15_04:00
daily_2018_06_14__00_00 hourly_2018_06_14__08_00  hourly_2018_06_14__20_00  hourly_2018_06_15__12_00
+
nfshomes_2018-06-14_16:00 nfshomes_2018-06-15_08:00
daily_2018_06_15__00_00 hourly_2018_06_14__12_00  hourly_2018_06_15__04_00  weekly_2018_06_09__00_00
+
nfshomes_2018-06-14_20:00 nfshomes_2018-06-15_12:00
 +
nfshomes_2018-06-15_00:00 Weekly_nfshomes_2018-06-10_00:00
 
</pre>
 
</pre>
Or this, on a ZFS filesystem:
+
 
 +
ZFS filesystem:
 
<pre>
 
<pre>
 
sattwood@swirl:~$ pwd
 
sattwood@swirl:~$ pwd
Line 51: Line 62:
 
zfs-auto-snap_hourly-2018-05-25-00h00  zfs-auto-snap_hourly-2018-06-15-12h00
 
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
 
zfs-auto-snap_hourly-2018-05-26-00h00  zfs-auto-snap_weekly-2018-06-09-03h00
 +
</pre>
 +
 +
FluidFS filesystem:
 +
<pre>
 +
sattwood@zaphod:~$ pwd
 +
/nfshomes/sattwood
 +
sattwood@zaphod:~$ cd .snapshots
 +
sattwood@zaphod:~/.snapshots$ ls
 +
daily_2018_06_14__20_00  hourly_2018_06_14__12_00  hourly_2018_06_15__04_00  weekly_2018_06_09__20_00
 +
daily_2018_06_15__20_00  hourly_2018_06_14__16_00  hourly_2018_06_15__08_00 
 +
hourly_2018_06_14__08_00  hourly_2018_06_14__00_00  hourly_2018_06_15__12_00 
 
</pre>
 
</pre>
  
 
For an example of file restoration, please see [[Snapshots:Example | this page]].
 
For an example of file restoration, please see [[Snapshots:Example | this page]].
 
 
[[Category:Snapshots]]
 
__NOTOC__
 

Latest revision as of 22:01, 6 December 2021

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 Isilon, 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 Retention Policy

Our core file systems in the department are on a 4 hour snapshot cycle.

Snapshot Name Retention Length When is it taken?
Hourly 24-32 hours Every day 12am, 4am, 8am, 12pm, 4pm
Daily 2 days Every day 8pm or 12am
Weekly 1 week Every Saturday 8pm or Sunday 12am

In other words, we retain up to either 6 or 8 hourly snapshots, 2 daily snapshots and 1 weekly snapshot. Hourly snapshots may be superseded by daily snapshots, and daily snapshots may be superseded by the 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 generally will not be visible, even when viewing hidden directories.

It will be either:

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

The inside of one of these will look like:

Isilon filesystem:

sattwood@coffee:~$ pwd
/nfshomes/sattwood
sattwood@coffee:~$ cd .snapshot
sattwood@coffee:~/.snapshot$ ls
nfshomes_2018-06-14_00:00  nfshomes_2018-06-15_04:00
nfshomes_2018-06-14_16:00  nfshomes_2018-06-15_08:00
nfshomes_2018-06-14_20:00  nfshomes_2018-06-15_12:00
nfshomes_2018-06-15_00:00  Weekly_nfshomes_2018-06-10_00:00

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

FluidFS filesystem:

sattwood@zaphod:~$ pwd
/nfshomes/sattwood
sattwood@zaphod:~$ cd .snapshots
sattwood@zaphod:~/.snapshots$ ls
daily_2018_06_14__20_00   hourly_2018_06_14__12_00  hourly_2018_06_15__04_00  weekly_2018_06_09__20_00
daily_2018_06_15__20_00   hourly_2018_06_14__16_00  hourly_2018_06_15__08_00  
hourly_2018_06_14__08_00  hourly_2018_06_14__00_00  hourly_2018_06_15__12_00  

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