Forum Discussion

mk128935's avatar
mk128935
Level 5
7 years ago

overwriting full backup in an incremental backup job

I have a customer who has a Windows server with a Tanberg Quikstation 8 emulated tape library attached. They want to run two backup jobs (one job taking full backups only, the other job taking increm...
20
Windows Server 2016
  • Colin_Weaver's avatar
    Colin_Weaver
    7 years ago

    Hmm Ok - so if using in tape emulation mode, we still don't do overwrites based on it filling up - it is still based on a timing that starts when the last data is written to the tape (and based on your PPT content you would have to allow an append period on the tapes for them to get close to full)

     

    We also have no way for the next job that starts to identify that the tape will fill during the activity of that instance of the job - so spanned sets will happen in your setup where the backup data ends up on two tapes/cartridges

     

    Oh and the reason for locking the full from being overwritten when there is a dependent incremental set now has to be managed manually by you as when a tape is overwritten it is the whole tape and not a specific backup set on the tape that is destroyed.

    GRT incremental sets still rely on the chain of incrementals back to and including the last full for a restore.

    Standard file system (non-GRT) sets of drive letter backups allow the resTore of files from just the specific incremental set (although for the the specific type of restore known as a point in time restore you do need the complete incremental chain back to the full)

     

     

     

Colin_Weaver's avatar
Colin_Weaver
Moderator
7 years ago

Disk based backup sets do not get overwritten, they get deleted (reclaimed) once they meet a combination of some DLM deletion/reclaim rules and the time based expiration criteria you set (and in the case of RDX when a backup jobs starts) We have no criteria that forces an overwrite when a cartridge is full.

There are also rules that link the incremental backups to the full backup. These rules means that the full cannot be deleted if there is a chain of incremental backups linked to it, if all incremental sets in the chain have not expired. You will also have problems with this rule if the incremental sets are on a removed/offline RDX cartridge when the full that you want deleted is on the active/online cartidge.

The last recovery chain (last full plus any linked incrementals will also not be deleted until a new recovery chain (so new full) has been run), although this can be on a different cartridge

One final point - GRT incremental sets require that the complete incremental and full chain is online when the next incremental runs so again means your strategy may have a problem.

The normal recommendation for RDX use is therefore run only full backups OR if you must run an incremental setup then these have to be written to the same cartridge as the full they depend on. Once you start with this as a concept, then you have to look carefully at the size and number of RDX cartridges in your rotation (taking into account last recovery set rule) as well as the expiration times of you full and incremental sets

Soem further info on RDX here:

https://vox.veritas.com/t5/Backup-Recovery-Community-Blog/Backup-Set-retention-and-expiry-Handling-on-Removable-RDX-etc/ba-p/788689.

 

  • mk128935's avatar
    mk128935
    Level 5
    7 years ago

    Thanks for the response. Sorry I should have been more clearer. Although this uses an RDX cartridge, the QuikStation 8 runs in tape emulation mode so it behaves just like a tape libarry. So the DLM rules wouldn't apply here but the tape media rotation rules would apply I would think.

    • Colin_Weaver's avatar
      Colin_Weaver
      Moderator
      7 years ago

      Hmm Ok - so if using in tape emulation mode, we still don't do overwrites based on it filling up - it is still based on a timing that starts when the last data is written to the tape (and based on your PPT content you would have to allow an append period on the tapes for them to get close to full)

       

      We also have no way for the next job that starts to identify that the tape will fill during the activity of that instance of the job - so spanned sets will happen in your setup where the backup data ends up on two tapes/cartridges

       

      Oh and the reason for locking the full from being overwritten when there is a dependent incremental set now has to be managed manually by you as when a tape is overwritten it is the whole tape and not a specific backup set on the tape that is destroyed.

      GRT incremental sets still rely on the chain of incrementals back to and including the last full for a restore.

      Standard file system (non-GRT) sets of drive letter backups allow the resTore of files from just the specific incremental set (although for the the specific type of restore known as a point in time restore you do need the complete incremental chain back to the full)