locked
How does WHS determine whether a cluster has changed? RRS feed

  • Question

  • Windows publishes at the file level two indicators of change, namely the time last modified and an archive(d) bit.  Does WHS use either of these to reduce its search for modified clusters?

    I ask this question to understand whether using some other backup product on a client PC to selectively backup key files to removable media for off-site storage would interfere with WHS's ability to maintain a full backup of my client PC.  Typically those desktop products use -- and reset -- the archive bit.  Can any of the inside tech gurus address whether this would affect WHS?

    Thanks!
    Tuesday, January 5, 2010 5:43 PM

Answers

  • DrumMemory:

    This is by no means an authoritative answer, but I don't think WHS backup is even looking at the file-level. The backup mechanism uses Volume Shadow Copy Service (VSS), and VSS is file-agnostic; it strictly looks for changes at the cluster level. So I doubt there will be any interference between backup software that utilizes the archive bit or the last modified date.
    Tuesday, January 5, 2010 7:13 PM
  • I've not noticed any interference other than both backup schemes use VSS and share the same Shadow Storage area on each volume. When a WHS backup occurs it needs to create a snapshot of the volume and the snapshot may bump out a few of the older shadow copies in the VSS storage area. As an example, on a PC that is not backed up by WHS I have daily Previous Versions of Files that extend back about 2 months in time. On a PC that is backed up by WHS the Previous Versions go back about a month.

    This would not affect the files-based Windows 7 backup where the output is a bunch of zip files.
    Tuesday, January 5, 2010 10:31 PM

All replies

  • DrumMemory:

    This is by no means an authoritative answer, but I don't think WHS backup is even looking at the file-level. The backup mechanism uses Volume Shadow Copy Service (VSS), and VSS is file-agnostic; it strictly looks for changes at the cluster level. So I doubt there will be any interference between backup software that utilizes the archive bit or the last modified date.
    Tuesday, January 5, 2010 7:13 PM
  • Might it interfere with the built-in Windows backup if the client is running Windows 7?
    Tuesday, January 5, 2010 7:28 PM
  • I've not noticed any interference other than both backup schemes use VSS and share the same Shadow Storage area on each volume. When a WHS backup occurs it needs to create a snapshot of the volume and the snapshot may bump out a few of the older shadow copies in the VSS storage area. As an example, on a PC that is not backed up by WHS I have daily Previous Versions of Files that extend back about 2 months in time. On a PC that is backed up by WHS the Previous Versions go back about a month.

    This would not affect the files-based Windows 7 backup where the output is a bunch of zip files.
    Tuesday, January 5, 2010 10:31 PM