VSS Full backup - how does it actually work?


  • Hello, this is something I cannot find a proper answer for:)

    Windows 10 Ent - VSS Full backup - how does it actually work? For some reason, when I set it up to be a full daily backup, it still only creates full backup first day, then runs incrementals next days.

    First day full backup takes around 1.3TB, I use 4TB backup drive. So I believe it should run 2 full backups, then start to delete older one to write new one and so on. Is that correct?

    I assume this is what it does as looking at the backup drive, first day it has 1.3TB, then next day was 1.35TB, so not another full backup.

    I thought VSS Full does FULL backup every time I schedule it, so if its daily, then it should run a full 1.3TB backups till fill up the drive then delete oldest to make new one?

    Monday, June 11, 2018 4:02 PM

All replies

  • Hi!

    The VSSFull doesn't mean full backup is performed.

    The command line definition help:

    Performs a full backup using the Volume Shadow Copy Service (VSS). Each file's history is updated to reflect that it was backed up. If this parameter is not used WBADMIN START BACKUP makes a copy backup, but the history of files being backed up is not updated.

    How Windows Server Backup works

    1) WSB uses VSS snapshot to take the consistent copy of the source volume.

    2) It copies the files or blocks from this snapshot to the backup-target.

    3) It creates a snapshot on the target to store a view of the backup on the target. (Any writes on the target will change the current copy but the backup can be accessed using the snapshot reference.)

    4) When next backup is initiated, 

    • In case Performance Setting is Faster performance: it just transfer the changed blocks, writing the changes on the target. Since the current copy contains complete data for recovery, the backup is still a full backup. There is no incremental chains and merging required for recovery.
    • In case Performance Setting is Slower performance: it again transfers all the blocks.

    When using the VSS Full, some applications stores there data in some log files which are perged at the backup time to give back better recoverability like Exchange, SQL where they would like to get some application level recoverability. VSSFull flag suggests that application should perge/close such data. Normally backup application use vsscopy with highger frequency than vssfull. For e.g. vsscopy every 30 minutes vssfull every day.

    Best regards,

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    Monday, June 11, 2018 4:35 PM
  • Thank you for your reply.

    So just to confirm I understand this - I simply run VSS full backup from backup wizard, I didn't use cmd lines to set it up. Chosen settings are:

    • Custom - to choose which volumes I want to back up
    • VSS full backup
    • normal backup performance
    • backing up to a volume (choosing USB ext drive)
    • daily backups

    What it does, it makes one full backup, then next day it makes a full back up again, however it overwrites the unchanged files, then makes a copy of files that have been changed as a second backup. This way I always have one bigger part that contains unchanged files, but is being written every day, then bunch of smaller parts, that are changed files batches, separate from each day.

    Is that correct?

    Ideally I would like to have this set up this way:

    • Monday - run FULL backup, all included
    • Tuesday, Wednesday, Thursday - differential backup only
    • Friday - run second FULL backup, all included - second backup, fully done all volumes
    • Saturday, Sunday - differentials to second backup only
    • Monday - run FULL backup, all included - overwrite prev Monday's backup as drive has only 4TB and full backup takes around 1.5TB

    How can I achieve this using Windows Server Backup?

    • Edited by phinix_mike Tuesday, June 12, 2018 11:12 AM
    Tuesday, June 12, 2018 8:36 AM