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How does VSS behave when there's low disk space?

    Question

  • Hi, I'm managing 2 SBS machines for small domains, one 2003 R2 and one 2008.

    VSS defaults to a set maximum size when enabled on a shared drive. That default may have been very sane when first installed, but over the months the user data grows to the point that there is low disk space on the machine (with many many GBs used by VSS).

    What happens in these curcumstances? I assume VSS reliquishes disk space, but at what rate, and how low does free space need to get before it does so?

    If VSS reliquishes space proactively, on a small network is it worth setting VSS Max Size to 100% thereby gaining the most historical data for online backup retreival, but not losing performance due to low disk space events?

    Thanks,

    Dom.

    Thursday, February 26, 2009 5:51 AM

Answers

  • Hi Dom,

    You are correct, the document does not seem to explicitly talk about this low disk space thingy. However, I would suggest you create your own Low Disk Space Alert (via PerfMon) in tandem with your VSS strategy.

    http://support.microsoft.com/kb/324796

    Let's hope this discussion gets into the MS folks' radar so that the docs get updated with the info you and I are seeking.

    Regards,

    Salvador Manaois III
    MCITP | Enterprise & Server Admin
    MCSE MCSA MCTS CIWA C|EH
    Bytes & Badz: http://badzmanaois.blogspot.com

    • Proposed as answer by David Shen Friday, February 27, 2009 6:13 AM
    • Marked as answer by PC Dom Monday, March 02, 2009 3:17 AM
    Friday, February 27, 2009 5:33 AM

All replies

  • Hi Dom,

    Afaik, VSS volume space defaults to 10% of the source volume. VSS will purge the oldest shadow copies when this allocated space is reached. You may want to look into hosting your shadow copies on a separate volume (where you can set the maximum size to No Limit) for better performance. Please refer to the following Technet article for a comprehensive look at designing a VSS strategy:

    http://technet.microsoft.com/en-us/library/cc728305.aspx

    Regards,

    Salvador Manaois III
    MCITP | Enterprise & Server Admin
    MCSE MCSA MCTS CIWA C|EH
    Bytes & Badz: http://badzmanaois.blogspot.com
    Thursday, February 26, 2009 6:13 AM
  • I've perused the document quickly a few times and can't find the answer to my question in it. Ultimate performance isn't an issue at the moment.

    Rephrasing: On a new server, VSS sets itself to 10% of the disk. What happens when user data has grown, so that there is only 5% of the disk free?

    Does VSS monitor disk space and delete shadow copies as free disk space becomes limited? What criteria does this occur in?

     

    I'm expecting VSS to have a threshold like "System Restore" in XP. If free disk space is reduced to below n%, VSS should delete shadow copies, starting with the oldest, to maintain n% free disk space. Eventually VSS will run out of copies to delete, and effectively be dissabled (300MB free disk space).

    Nothing in "Designing a VSS Strategy" mentions low disk space, which seems to be a big gap in the documentation.

    Thanks!

    Friday, February 27, 2009 12:49 AM
  • Hi Dom,

    You are correct, the document does not seem to explicitly talk about this low disk space thingy. However, I would suggest you create your own Low Disk Space Alert (via PerfMon) in tandem with your VSS strategy.

    http://support.microsoft.com/kb/324796

    Let's hope this discussion gets into the MS folks' radar so that the docs get updated with the info you and I are seeking.

    Regards,

    Salvador Manaois III
    MCITP | Enterprise & Server Admin
    MCSE MCSA MCTS CIWA C|EH
    Bytes & Badz: http://badzmanaois.blogspot.com

    • Proposed as answer by David Shen Friday, February 27, 2009 6:13 AM
    • Marked as answer by PC Dom Monday, March 02, 2009 3:17 AM
    Friday, February 27, 2009 5:33 AM
  • I'd just like to point out that the VSS documentation has been missing information on "Low Disk Space" behaviour since 2003. Neither the Server 2003 nor 2008 documentation details what happens in this case.

    This is an incredible oversight as, in my mind, it would be a reasonably common occurrence.

    5+ years to write 1 paragraph about what the program actually does seems pretty poor form!
    Monday, March 02, 2009 3:17 AM