Subscribe

Determining snapshot content

Hi everyone,

We noticed that our Saturday morning snapshots have been running around 1 TB, which is already quite large compared to all the other snapshots, but last Saturday's snapshot was over 3 TB, which is truly excessive. We have been using filesystem-level tools to try to determine where the growth came from, but I wanted to check in here and see if anyone knows of any tools or techniques which might show us what changed.

Thanks,

Tom

Re: Determining snapshot content

Hi Tom,

Can you share with us the type of data being stored in that particular volume?

1-3TB snapshot is really big, what is the total size of the volume in question?

Regards,

Pedro Rocha

Re: Determining snapshot content

Well ... Snapshots also "grow" when you delete files from active filesystem or overwrite them. So using host- level tools you may well see the same or even reduced total size. It is change rate that matters.

Re: Determining snapshot content

The total allocated space for the volume is about 13 TB, with a 20% snap reserve, and the data is regular file data.

Re: Determining snapshot content

Tom,

You need to check with the respective DBA team or the server team who ever have a Idea on what might have caused at the bigger snapshot time frame. Use System manager software for good info on snapshot sizes and graph representation.

1. If the amount of space used by snapshots increases, even though the amount of used storage by the files remains unchanged, we could assume that existing files in the volume are undergoing a high rate of change.

2. A large increase in the size of snapshots could also indicate the deletion of files, since a deleted file isn't really deleted until every snapshot referencing the file is removed.  The increase in the snapshot size should have a correlating decrease in the main filesystem when a file is deleted.

3. It could be possible for the snapshot storage used to exceed the filesystem storage used based on the rate of change in files, or depending on how old the accumulated snapshots are.  Monitoring the size of the snapshots can be a good way to determine how large your snapshot reserve should be.

4. Decreases in snapshot consumption are likely an indication of snapshots being rotated out, or removed from the volume.

Hope it helps!

Regards,

RK

Re: Determining snapshot content

You can use snap delta command... may be help you to get data changes rate b/w snapshot on problematic volume..

Snap delta volume name