Archive Bit Vs. Modified Time

Posted on 2007-07-25
Last Modified: 2013-12-01
With Backup Exec 10.0, what are the advantages and disadvantages of using Archive Bit vs. Modified Time for full and incremental backup, and do  these options have any effect specifically to backing up Exchange Mailboxes.  

I am concerned about the size of my backup jobs. The full backup of my mailboxes are 135 GB, and the incremental is 100 GB. Should I not be seeing much smaller backups for my incremental?
Question by:ejunge
    LVL 28

    Expert Comment

    Assume that all data has changed, then the sizes would be almost equal, so if most of tha data has changed they're almost equal in size.
    Full backup doesn't care for the file time or archive bit, it just copies the lot to the backup media.
    Archive bit tells that the file has been modified since an undefined time in the past so BE will grab it to the backup. You have two options here, one to reset archive bit and one to keep it. If you reset it and the file is not changed at the time of the next incremental backup it will not be included. I believe that's the option you want.

    File modification time will make BE compare the file time on disk with that on the backup media (takes longer)

    LVL 104

    Expert Comment

    If you are backing up mailboxes instead of the information store then I am not surprised you are concerned about the backups.
    However mailbox backups are close to useless for most disaster recovery scenarios. When it comes to Exchange I never do incremental backups, only full backups.

    LVL 28

    Expert Comment

    sembee, backing up mailboxes? You mean the old brick level ?
    LVL 104

    Expert Comment

    Brick level backup. When i see someone say mailboxes instead of information store that is what I tend to think of.

    LVL 28

    Expert Comment

    OK, we don't use that anymore :)
    LVL 23

    Accepted Solution

    Archive bit and Modified Time is almost the same
    no effect on Exchange as there you backup the Transaction logs
    the feature is there so that you can select the option for modified time where there are no Archive bits

    Archive Bit

    Whenever a file is created or changed, the operating system activates the Archive Bit or
    modified bit. Unless you select to use backup methods that depend on a date and time
    stamp, Backup Exec uses the archive bit to determine whether a file has been backed up,
    which is an important element of your backup strategy.
    Selecting the following backup methods can affect the archive bit:
      Full - Back up files - Using archive bit (reset archive bit)
      Differential - Back up changed files since last full - Using archive bit (does not reset
    archive bit)
      Incremental - Back up changed files since last full or incremental - Using archive bit
    (reset archive bit)
    Whenever a file has been backed up using either the Full - Back up files - Using archive
    bit (reset archive bit) or Incremental - Changed Files - Reset Archive Bit backup
    method, Backup Exec turns the archive bit off, indicating to the system that the file has
    been backed up. If the file is changed again prior to the next full or incremental backup,
    the bit is turned on again, and Backup Exec will back up the file in the next full or
    incremental backup. Backups using the Differential - Changed Files backup method
    include only files that were created or modified since the last full backup. When this type
    of differential backup is performed, the archive bit is left intact.

    Modified Time
    If you select to use Full - Back Up Files - Using modified time, Differential - Using
    modified time, or Incremental - Using modified time, Backup Exec uses a files modified
    time rather than the archive bit to determine if it needs to be backed up.
    When Backup Exec runs a full or incremental backup, the time the backup launches is
    recorded in the Backup Exec database. The next time an incremental or differential
    backup launches, Backup Exec compares the file system time to the backup time recorded
    in the Backup Exec database. If the file system time is later than the database time, the
    file is backed up.
    Note The Full - Using modified time backup method adds the time of the backup to the
    Backup Exec database only if the full backup job completes successfully. If the full
    backup job does not complete successfully, any subsequent backup jobs that use
    the differential or incremental modified time backup methods back up all of the
    data instead of just the data that changed since the last full backup.
    About backup strategies
    When an incremental backup is run, a new time is recorded in the Backup Exec database.
    The database time is not updated with differential backups.
    Using the modified time allows Backup Exec to run differential backups on file system,
    such as Unix, which do not have an archive bit.
    If you want Backup Exec to use modified time to determine if a file has been backed up,
    the full and incremental (or full and differential) backups must use the same backup
    selection list.
    LVL 1

    Expert Comment

    Forced accept.

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