SMVI snapshot unexpectedly large

[drwoodberry]

We are currently running VSC 4.2.1P1 with DataOntap 8.1.4P2. We just upgraded to 8.1.4P2 actually. After doing this, we noticed that our iSCSI VMFS datastores SMVI snapshots are huge. The snapshots before the upgrade were in the 1-3 GB size. After they are almost 500GB. We have not had any unexpected data growth on the VM's in question. We also noticed when we deleted the most recent SMVI snapshot, the next newest snapshot size grew to the same size. We saw this same thing happen at two different sites with only the iSCSI VMFS datastores. The NFS datastores did not show this behavior. Looking at what was being backed up before and after the upgrade, the datastore contents were the same.

Thoughts, Comments?

[sahil_anand]

Did you guys tried reallocate on affected luns recently before or after upgrade? and deleting the last snapshot will help reducing the amount of space snapshot are taking up. 

[drwoodberry]

We did not try a reallocate before or after the upgrade. When we deleted the last snapshot, most recent, the snapshot before that would then grow. It makes no sense. Are retention periods are not that long. It is odd why an older snapshot would grow after deleting a more recent one.

[sahil_anand]

It's not odd, snapshots are designed in such a way; if you delete the recent one, older ones will grow in size, they will have all the data from deleted(recent) snapshot, which causes size increase. Hope this helps. 

Thanks,

Sahil

[drwoodberry]

Thanks for the response, I guess I had just never noticed it before. When I think of snapshot, I think of a moment in time instance of the storage. I was not aware there were ways to make the snapshot larger or smaller. Once it was taken, I thought it was taken, but I guess since they are just pointers to blocks, all those pointers are updated??? This makes the next previous snapshot larger??

[sahil_anand]

well, what you said true, snapshot is point in time copy.  baseline snapshot acts as root pointer to blocks, so until baseline snapshot is not deleted you wont see free space. Deleting later snapshots will only add to bigger size of baseline snapshot and updating all those pointers, infant just adding more pointer to baseline snapshot.

[drwoodberry]

Any reason why we would see such a large snapshot thought after this initial upgrade? Do you think a new "baseline" snapshot was taken?

[sahil_anand]

I think baseline snapshot could be a reason, but there are many other factors that can be culprit. 2-3 GB snapshot should not have zoomed to 500 GB of size, From which version you had upgraded your ONTAP to 8.1.4P2?

[drwoodberry]

We came from 8.1.2 on these systems