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Tape Back Question

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  • Tape Back Question


    I am trying to come up with a new tape rotation schedule.

    If we implement, weekly full backup say on Friday, while we do differential backups during the week.

    My question is on the recoverable data.

    Say we are in 3rd week, Monday and the previous week’s full backup tape doesn’t work (corrupt). Can we go the the 1st week full backup and use the 2nd week’s differential tape from Thursday?

    Or does the fact that you do a “full” backup on Friday, reset all your differential tapes to reference the last full back up – and ignore previous full backup tapes?


  • #2
    Re: Tape Back Question

    While the answer may depend on which backup software you're using... I would guess that the failure of Friday's full backup would be a problem. I usually recommend to people that their offsite backup should be a full backup each night if possible.
    Gareth Howells

    BSc (Hons), MBCS, MCP, MCDST, ICCE

    Any advice is given in good faith and without warranty.

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    • #3
      Re: Tape Back Question

      It's simple and it's complicated.

      Here's the simple part: Every Full backup resets the archive bit so your differential backups are dependent on specific Full backups. For instance, a Full backup is done on Monday and a Differential is done on Tuesday. Another Full backup is done on Wednesday and another Differential is done on Thursday. Thursday's Differential is based on Wednesday's Full backup, not Tuesday's.

      Here's the complicated part: You may find yourself without the ability to restore a specific set of files or a particular system if Tuesday's Full backup is corrupt and you need Tueday's Full backup and Wednesday's Differential backup in order to restore that particular set of files or that particular system.

      That's not to say all is lost as Wednesday's Full and Thursday's Differential likely have what you need to restore a particular set of files or a particular system. In my experience I've never had to rely on both the latest Full and the latest Differential backup in order to restore a particular set of files or a particular system. IMHO, 999 times out of 1,000 you're going to be restoring individual items (files, documents, emails, etc.) and not entire directories or entire systems. In 10 years of working in IT I've had to restore an entire directory or an entire system less than 5 times.

      Here's how I protect my systems:

      1. I run a Full file system backup of every server on Saturday.

      2. I run an incremental file system backup of every server the remaining 6 days of the week.

      3. I run a Full System State backup of every server every day.

      4. I use the Previous Versions capability on my file servers. I set it to capture every 4 hours from 8AM until 8PM. I set the Previous Versions disk limit to about 10% of the total drive space.

      5. I use a product called UnDelete on my file servers. It catches all file deletes on the file server whether they're done locally or over the network. I set the disk limit to about 10% of the total drive space.

      It may seem like overkill, but it's a pretty rare event if I can't restore an item using one of the three technologies above.


      • #4
        Re: Tape Back Question

        Thank you.

        You have provided a detailed and very nice answer.


        • #5
          Re: Tape Back Question

          Glad to help.