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Netuk's avatar
Netuk
Level 3
11 years ago

Tape management in Netbackup

Hi,


I have a problem of Managing Tapes. We use LTO4 Tapes, It can retain 3TB in compressed format;
(1) we use NDMP backups from NetApp directly to tape
(2) I have checked "Allow multiple retention per media"
(3) Still we get 1TB - 3TB data in a single tape and Tape shows Full.
(4) Additionally I get different backup speeds for each NetApp Volume backup, even from the same NetApp filer.

I am finding ways to have a consistent backup but difficult to get due to above problems. Pls help to resolve these problems.

3 Replies

  • First, just confirm that you have no software compression enabled in the policy - if you do not, then the below details are true.  If you do, turn it off and try again.

    NBU only marks the tape full when it is told to by the taoe driver.

    The tape drive firmware detects the logical end of tape (a 'marker' written to the tape during manufacture) - it then sets a flag in the the driver,

    The tape driver then 'alerts' NetBackup that the tape is full.  Only then does NBU actually mark the tape as full and swap to a new one.

    Therefore, there is nothing that can be done in NBU to address tapes being marked full - absolutely no control over this at all. 

    Either.

    The tape really is full

    There is a tape drive fault

    There is a tape firmware or driver issue

    Tapes only manage a high amount of data, if that data is compressable - some data is, some data isn't.

    Eg.  .txt files will compress really well.

    .jpg files don't, as .jpg is already a compressed format.

    Different speeds from different volumes on the same filer would suggest simply that the different volumes can supply data at different speeds, that is, the read speed of the disk.

    I would say that on average 1 - 3TB on the tape would be 'expected' if you have a range of data that has different 'compressability'.

    If you believe there is still an issue with the amount of data on the tape, you will need to address this with the manufacture of the tape drives.  As mentioned, there is nothing in NetBackup that can be done.

    It might be worth running a Full erase on the tapes (only when they have expired) and retrying them - I haven't known this to be a cause of this issue persoanlly, but depending on the drive firmware it may re-initialise the chip inside the tape.  Worth a go.

     

  • (2) I have checked "Allow multiple retention per media"

    This option seems like a good idea initially, but causes tape availability issues in the long run.
    Bear in mind that ALL images on a tape must expire before NBU can reuse it.
    So, when short retention images start to expire, the space cannot be reused.

    Have a look at this excellent blog: 
    Understanding how NetBackup writes to a tape. 
     

    (4) Additionally I get different backup speeds for each NetApp Volume backup, even from the same NetApp filer.

    This will depend on how fast the filer can read the data from disk.
    Lots of files with lots of directory levels will take filer a long time to 'walk' the filesystem in order to generate the backup stream.

    To test, use NetApp OS tools such as tar to backup to /dev/null. Record the time that it takes. 

  • HI mph999/Marianne,

    As mph999 told some of the volumes have deduplication enabled on NetApp and that might make the read to tape take long. We have not enabled compression from from Netbackup. Its just compression from Tape drive itself.

    As Marianne told I have opened a support case with NetApp and let you know the results.

    I will update with the findings from NetApp side.