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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 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 [[NightlyBackups | full backups]].


We provide [[Snapshots]] on our [[ONStor]] and [[SnapshotsNexenta | Nexenta]] filers to certain file systems.
We provide snapshots on our Isilon, ZFS, VAST, and Qumulo filers to certain file systems. If you are ever unsure if a particular volume has snapshots enabled, please contact the [[HelpDesk | Help Desk]].


Please see [[SnapshotFileSystems]] for a list of our file systems that have snapshots in the department.
==Snapshot Retention Policy==
Our core file systems are on a 4 hour snapshot cycle.


==Snapshot Policy==
{| class="wikitable"
 
!Snapshot Name
Our core file systems in the department are on a 4 hour snapshot cycle.  Snapshots are taken at,
!Retention Length
 
!When is it taken?
{| style="color:green; background-color:#ffffcc;" cellpadding="5" cellspacing="0"
|-
| 12am
|'''Hourly'''
| 4am
|24-32 hours
| 8am
|Every day 12am, 4am, 8am, 12pm, 4pm
| 12pm
|-
| 4pm
|'''Daily'''
| 8pm
|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 Hourly snapshots may be superseded by daily snapshots, and daily snapshots may be superseded by the weekly snapshot.
 
These are available on the following [[OpenLAB]] file systems,


==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.  It generally will not be visible, even when viewing hidden directories.


If you find that you have mistakenly deleted a file and it was created/written to before the last snapshot[1].  You can restore the file by going to the directory where the file was and changing into the .snapshot directory and then using a normal copy operation to copy it back to the directory where you would like it. Please note that the .snapshot directory is hidden and may not appear when you do a directory listing.
'''It will be either''':
 
* .snapshot for the Isilon, VAST, or Qumulo filers
''[1] - If a file was created or modified after the last snapshot then you can potentially lose up to 4 hours of work in a worse case scenario.  Please make sure you save your work throughout the day.''
* .zfs/snapshot for the ZFS filer


Example:
The inside of one of these will look something like:


Changing to my quotes directory.
Isilon filesystem:
<pre>
<pre>
[derek@novelty quotes]$ pwd
$ pwd
/nfshomes/derek/work/quotes
/nfshomes/username
$ cd .snapshot
$ ls
nfshomes_2024-09-14_00:00  nfshomes_2024-09-16_04:00                         
nfshomes_2024-09-15_00:00  nfshomes_2024-09-16_08:00                         
nfshomes_2024-09-15_16:00  nfshomes_2024-09-16_12:00                         
nfshomes_2024-09-15_20:00  Weekly_nfshomes_2024-09-08_00:00                   
nfshomes_2024-09-16_00:00  Weekly_nfshomes_2024-09-15_00:00
</pre>
</pre>
I see that i have a quote called  '''redhat_sole_source_2007.doc'''.
 
<pre>
ZFS filesystem:
[derek@novelty quotes]$ ls
dlt_pdf_quote2007.pdf  Quote_300086759.html        redhat_solesource.pdf
dlt_pdf_quote.pdf      Quote_353511914.html        soleSource2007.pdf
dlt_quote.pdf          Quote_367512608.html        soleSource.pdf
dy1014.xls            Quote_367884529.html        UMD_008.xls
Quote_250530976.html  redhat_sole_source_2007.doc
</pre>
<pre>
[derek@novelty quotes]$ ls -la redhat_sole_source_2007.doc
-rw-r--r-- 1 derek derek 39936 Jan 23  2007 redhat_sole_source_2007.doc
</pre>
I will remove it from the current file system.
<pre>
[derek@novelty quotes]$ rm redhat_sole_source_2007.doc
</pre>
As you can see it no longer is there.
<pre>
[derek@novelty quotes]$ ls
dlt_pdf_quote2007.pdf  Quote_250530976.html  Quote_367884529.html  UMD_008.xls
dlt_pdf_quote.pdf      Quote_300086759.html  redhat_solesource.pdf
dlt_quote.pdf          Quote_353511914.html  soleSource2007.pdf
dy1014.xls            Quote_367512608.html  soleSource.pdf
</pre>
I am going to go into the last hourly snapshot '''hourly.0'''
<pre>
[derek@novelty quotes]$ cd .snapshot/hourly.0
</pre>
As you can see the quote is still here.
<pre>
<pre>
[derek@novelty hourly.0]$ ls
$ pwd
dlt_pdf_quote2007.pdf Quote_300086759.html        redhat_solesource.pdf
/nmhomes/username
dlt_pdf_quote.pdf      Quote_353511914.html        soleSource2007.pdf
$ cd .zfs/snapshot
dlt_quote.pdf          Quote_367512608.html        soleSource.pdf
$ ls
dy1014.xls            Quote_367884529.html        UMD_008.xls
zfs-auto-snap_daily-2024-09-14-2000  zfs-auto-snap_hourly-2024-09-16-0000   
Quote_250530976.html  redhat_sole_source_2007.doc
zfs-auto-snap_daily-2024-09-15-2000  zfs-auto-snap_hourly-2024-09-16-0400   
zfs-auto-snap_hourly-2024-09-15-0400 zfs-auto-snap_hourly-2024-09-16-0800   
zfs-auto-snap_hourly-2024-09-15-0800  zfs-auto-snap_hourly-2024-09-16-1200   
zfs-auto-snap_hourly-2024-09-15-1200  zfs-auto-snap_weekly-2024-09-14-2000   
zfs-auto-snap_hourly-2024-09-15-1600
</pre>
</pre>
I copy it back to the original directory.
<pre>
[derek@novelty hourly.0]$ cp redhat_sole_source_2007.doc /nfshomes/derek/work/quotes/
</pre>
Change back to the original directory.
<pre>
[derek@novelty hourly.0]$ cd /nfshomes/derek/work/quotes/
</pre>
And it is back.
<pre>
[derek@novelty quotes]$ ls
dlt_pdf_quote2007.pdf  Quote_300086759.html        redhat_solesource.pdf
dlt_pdf_quote.pdf      Quote_353511914.html        soleSource2007.pdf
dlt_quote.pdf          Quote_367512608.html        soleSource.pdf
dy1014.xls            Quote_367884529.html        UMD_008.xls
Quote_250530976.html  redhat_sole_source_2007.doc
</pre>


[[Category:Snapshots]]
For an example of file restoration, please see [[Snapshots:Example | this page]].
__NOTOC__

Latest revision as of 19:50, 16 September 2024

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, VAST, and Qumulo 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 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. It generally will not be visible, even when viewing hidden directories.

It will be either:

  • .snapshot for the Isilon, VAST, or Qumulo filers
  • .zfs/snapshot for the ZFS filer

The inside of one of these will look something like:

Isilon filesystem: 

$ pwd
/nfshomes/username
$ cd .snapshot
$ ls
nfshomes_2024-09-14_00:00  nfshomes_2024-09-16_04:00                           
nfshomes_2024-09-15_00:00  nfshomes_2024-09-16_08:00                           
nfshomes_2024-09-15_16:00  nfshomes_2024-09-16_12:00                           
nfshomes_2024-09-15_20:00  Weekly_nfshomes_2024-09-08_00:00                    
nfshomes_2024-09-16_00:00  Weekly_nfshomes_2024-09-15_00:00

ZFS filesystem: 

$ pwd
/nmhomes/username
$ cd .zfs/snapshot
$ ls
zfs-auto-snap_daily-2024-09-14-2000   zfs-auto-snap_hourly-2024-09-16-0000     
zfs-auto-snap_daily-2024-09-15-2000   zfs-auto-snap_hourly-2024-09-16-0400     
zfs-auto-snap_hourly-2024-09-15-0400  zfs-auto-snap_hourly-2024-09-16-0800     
zfs-auto-snap_hourly-2024-09-15-0800  zfs-auto-snap_hourly-2024-09-16-1200     
zfs-auto-snap_hourly-2024-09-15-1200  zfs-auto-snap_weekly-2024-09-14-2000     
zfs-auto-snap_hourly-2024-09-15-1600

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

Retrieved from "https://wiki.umiacs.umd.edu/umiacs/index.php?title=Snapshots&oldid=12025"