VSS is deleting all copies rather than just the oldest one

Question

I have dedupe enabled on my data server volumes - the optimization task runs in the background throughout the day and throughput optimization for x9 hours each evening, the garbage collection job each week and a full on the 4th run time...

The data volumes on the server have corresponding allocated volumes for which VSS is enabled and takes snapshots of the data volumes twice per day - the VSS is set to no limit.

Since enabling dedupe it appears that VSS deletes all of the snapshots of the data - please see below from the event log;

I see these events being logged within a 30 minute timeframe of each other - these snapshots are being deleted outside of the configured VSS schedule - the result for all the VSS volumes on the data server are that we're left with an empty volume with no real data there at all!

Our thoughts are that due to the optimization tasks which are running this is creating a large number of unreferenced file chunks - we then need to wait for the garbage collection job to run which takes place once per week for the unreferenced chunks to be removed so VSS doesn't just create a copy of these unreferenced chunks which is empty data.

Before implementing data dedupe I reviewed the MS documentation for using dedupe and VSS - the main thing is that we are not using VSS on the same volume as the data, if so then we would be unbale to use data dedupe - do you know if it's possible to prevent VSS from copying unreferenced chunks of data before the garbage collection runs?

A potential work around to this would be to run the garbage collection job more frequently so there's not so many unreferenced chunks for VSS to backup? It would also be worth reducing the optimization job runs as well as each time this runs more unreferenced chunks are created which in turn increases the storage space required for the VSS volume...

Please let me know your thoughts on how to mitigate this issue from re occurring?

Answer 1

Hi Russeller，
For the error code you might refer to this:
https://kb.eventtracker.com/evtpass/evtpages/EventId_33_VolSnap_47346.asp
Please note: Information posted in the given link is hosted by a third party. Microsoft does not guarantee the accuracy and effectiveness of information.

Based on my understanding, VSS will delete the oldest copies first, and will continue to delete as many copies as it needs in order to have enough space to make a new copy or when the I/O is too high. It‘s like a default behavior of it. And it is probably what’s happening in your case, VSS is just working as designed.

To deal with this，I would suggest that you expand the volume or lower down the I/O.

Thanks for your understanding.
Best Regards,
Danny

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