Feedback requested on proposed snapshot strategy

[Andrew Kaplan]

Hello --

I have been asked by my supervisor to get feedback on a snapshot strategy. Currently we have a lefthand configuration where a weekly snapshot is done on the primary array, and is subsequently copied over to the secondary array. The primary lefthand keeps one snapshot at a given time, while the secondary keeps a total of three. The snapshots are done weekly. The volume in question on the primary array is eight terabytes, while that on the secondary array is roughly twelve terabytes.

The most recent snapshot that is one the secondary gets mounted, via iSCSI, to a Windows server, and that newly mounted drive gets backed up to tape. This process occurs weekly. The snapshots in question are about four terabytes in size. The two arrays are configured with overprovisioning.

The strategy that is being proposed is the following:

1. Have the snapshots complete as they are done now.

2. Instead of having three snapshots on the secondary, retain only one at a given time.

3. Once the tape backup is complete, delete the snapshot that is on the primary.

The purpose behind this is to recover as much space as possible without too much risk of lost data.

Feedback on this strategy would be appreciated.

[oikjn]

snapshots are NOT backups.  It appears that is what you are trying to do and that is not a good idea.  It isn't a reliable backup solution because it relies on the initial data+change information and that means if the initial data gets corrupted then you are screwed.

In general snapshots have two uses (ignoring a basic file server situation).  A quick restore point to make a temporary undo point when making a change to the system you feel is risky and needs a quick "undo" safety net.  And, a way for your back program to freeze the data to make a consistent backup...  neither situation should result in the snapshot lasting for more than a few days at max. 

I can't really give any specific advice without knowing the backup solution and basic site setup, but I"m guessing what you want to be doing is backup the system and then ship that backup off-site, which really has nothing to do with sending the snapshot off-site.  IF you have a remote site with sufficient bandwidth, you can use remote snapshots to create a remote volume, but if you are concerned about space on your primary site, you will need to do more frequent snapshots and keep only one locally so that the change data between the snapshots is minimized.