question

TheRusseller1-3951 avatar image
0 Votes"
TheRusseller1-3951 asked YuhanDeng-MSFT commented

VSS is deleting all copies rather than just the oldest one

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;

119114-image.png




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?


windows-server
image.png (89.3 KiB)
· 3
5 |1600 characters needed characters left characters exceeded

Up to 10 attachments (including images) can be used with a maximum of 3.0 MiB each and 30.0 MiB total.

Hi Matt,

I would like to check if the reply could be of help? If yes, please help accept answer, so that others meet a similar issue can find useful information quickly. If you have any other concerns or questions, please feel free to feedback.

Best Regards,
Danny

0 Votes 0 ·

@DanielZhang-MSFT I'm slightly reluctant to mark your reply as an answer to the solution as you have just agreed to my logical approach which may work to resolve the issue.

0 Votes 0 ·

Hi Matt,
As I mentioned in the reply 2 days ago. Since I cannot reproduce the issue in my environment, I cannot guarantee the outcome of your trial.
Please do make copies of your data before you try it.

Thanks for your reply.
Best regards,
Danny

0 Votes 0 ·

1 Answer

YuhanDeng-MSFT avatar image
0 Votes"
YuhanDeng-MSFT answered YuhanDeng-MSFT commented

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


If the Answer is helpful, please click "Accept Answer" and upvote it.

Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.

· 2
5 |1600 characters needed characters left characters exceeded

Up to 10 attachments (including images) can be used with a maximum of 3.0 MiB each and 30.0 MiB total.

@YuhanDeng-MSFT thanks for your comment - yes agreed VSS should only be removing the oldest snapshot first...

I'm trying to look at this issue and potential resolution with a more logical approach...okay so MS do say VSS is supported with dedupe enabled provided VSS is not being used on the same volume as what the dedupe tasks are.

  1. We could increase the garbage collection scheduled task to run more frequently - this would remove the unreferenced file chunks from the dedupe enabled volume which would result in VSS not creating snapshots of blank data

  2. The VSS schedule could be increased - we currently run this twice per day - by increasing the snapshot frequency this would mean we'd obviously have more snapshots however not all of the snapshots would be deleted depending on how much optimization is done on the volumes be dedupe running. For example currently the x2 snapshots are two large snapshots when VSS runs again the new copy size is the size of both of the snapshots - having more smaller snapshots would mean some of the snapshots are deleted but others will remain - this in time will decrease as the dedupe enabled volume becomes fully deduped


Keen to know your thought's on this.

Thanks,

Matt



0 Votes 0 ·

Hi Matt,
Sounds like a good resolution to me. However, since I cannot reproduce the environment here in my lab, I cannot garuatee it.
I would suggest that you try it in your environment and see what happens. Please do make copies of your machines in case of unexpected errors.

Thanks for your understanding,
Best regards,
Danny

0 Votes 0 ·