Forum Discussion

James_Khor's avatar
James_Khor
Level 2
11 years ago

Separate media pool for differential and full backup

Should there be separate media pool for daily differential and weekly full backup job? The pros: 1. Minimize the loss of data as a result of tape failure 2. Any other benefits? The cons: 1. Unproductive usage of tapes 2. More tapes are required 3. Longer recovery time as different set of tapes are required. Currently, I am in a dilemma after I have a conflict of ideas with the subject matter expert (SME) in my company. I support separate media pool but the SME supports a media pool for both type of jobs. So I like to find out what is the industry practice, and also to know more about the pros and cons before making an objective comparison, in order to recommend to my client. Cheers.

7.5
Backup and Recovery
NetBackup
Windows Server (2003-2008)
  • Jim-90's avatar
    Jim-90
    11 years ago

    Your assumption are

    The pros:
    1. Minimize the loss of data as a result of tape failure     - the probability of anything happening to a tape tape is the same irrespective of media pool. They will be separated because of different retention periods - see previous post and below
    2. Any other benefits?  Probably none, apart from trying to ensure continance employment through work creation

    The cons:
    1. Unproductive usage of tapes -     You avoid this by setting the Max number of partially filled media on the property of each Volume Pool.  Personally I would not permit the maximum to be any more than : the number of tape drives X the number of different retention periods +1.  Depends on how many tape drives you have to play with.
    2. More tapes are required. Nope because I wouldn't bother separating them.  Let the automagic of NBU take care of it. I don't see any reason to make things more complicated than they are.
    3. Longer recovery time as different set of tapes are required.  Nope see previous. 

    The full backups should be at least one time period longer that the non-full backups.

    • If the retention period of the non-fulls is fours weeks then then the minimum retention of fulls should be five weeks
    • If the retention period of the non-fulls is one  month then then the minimum retention of fulls should be two months. 
    • etc

    Why :

    When a full backup is deleted from the system there should no non-full backups dependent upon it.

    If you have the fulls and non-fulls with the same retention period you will waste backup storage because you could have a lot of non-fulls backups that are useless because there is no full backup base to restore.  From the previous example that means either one week or one month of non-full backups.  

     

     

     

     

     

  • Marianne's avatar
    Marianne
    Level 6
    11 years ago

    NetBackup does not mix retention levels, even if written to the same pool.
    So, your Incr and Full backups will in any case land on different tapes.

    Multiple retentions can be allowed per media, but it is not recommended, as media can only be recycled/overwritten when all images have expired.
    So, if you happen to have a tape with mostly Diff Inc on it with short retention level (e.g. 2 weeks) and one Full backup with 6 months retention, the space used by the Diff Inc cannot be overwritten when they expire. Media can only be appended to. So, this tape can only be overwritten when the last Full backup has also expired.
    Multiple retentions seems like a good idea as a short-term solution, but will end up using more tape.

    See this excellent blog: Understanding how NetBackup writes to a tape. 

    Having disk for Diff Inc is a better option.
    Not only will restores be quicker for the regular 'oops factor' restores, backups may also be quicker and space can be reclaimed as and when Diffs expire.
    Naturally a good idea to stage to tape if all backups must be kept offsite.

    The only advantage to having different pools for Diff and Full is that they are easy to identify.
    A quick glance at each pool will tell you if you have enough media for upcoming backups.
    But if you have a Scratch pool you don't need to manually monitor each pool.

    So, in short - Diff Inc over Cumm Inc backups will always have the disadvantage of longer restores as the last full and all Diffs are needed for restores.
    Cumm Inc will only need last Full and last Cumm Inc.

    PS:
    You may want to discuss Dedupe options with your customer, as this is the direction that the world is moving...

  • Jim-90's avatar
    Jim-90
    Level 6
    11 years ago

    Your assumption are

    The pros:
    1. Minimize the loss of data as a result of tape failure     - the probability of anything happening to a tape tape is the same irrespective of media pool. They will be separated because of different retention periods - see previous post and below
    2. Any other benefits?  Probably none, apart from trying to ensure continance employment through work creation

    The cons:
    1. Unproductive usage of tapes -     You avoid this by setting the Max number of partially filled media on the property of each Volume Pool.  Personally I would not permit the maximum to be any more than : the number of tape drives X the number of different retention periods +1.  Depends on how many tape drives you have to play with.
    2. More tapes are required. Nope because I wouldn't bother separating them.  Let the automagic of NBU take care of it. I don't see any reason to make things more complicated than they are.
    3. Longer recovery time as different set of tapes are required.  Nope see previous. 

    The full backups should be at least one time period longer that the non-full backups.

    • If the retention period of the non-fulls is fours weeks then then the minimum retention of fulls should be five weeks
    • If the retention period of the non-fulls is one  month then then the minimum retention of fulls should be two months. 
    • etc

    Why :

    When a full backup is deleted from the system there should no non-full backups dependent upon it.

    If you have the fulls and non-fulls with the same retention period you will waste backup storage because you could have a lot of non-fulls backups that are useless because there is no full backup base to restore.  From the previous example that means either one week or one month of non-full backups.  

     

     

     

     

     

  • Marianne's avatar
    Marianne
    Level 6
    11 years ago

    James is a new Connect member who posted once and has not been back since 1 May to check for answers/updates....