Forum Discussion

solomοn's avatar
solomοn
Level 3
2 years ago

tape capacity

what im facing is that i move from a pool some tapes, create a new pool, and i have add that tapes

now the problem is that tapes are not being filled to capacity

on 50-60% of the tapes capacity the policy start mounting a new tape from the same pool and the first tape shows as full

if i run the same policy on other pool this is not happen even that tape from the other pool had less free space

if i check for images on that tape there are only the new not previous images from the old pool

has anything to do with a configuration i missed ?

  • Mxyda's avatar
    Mxyda
    2 years ago

    good explanation , thanks for the info guys ,

    i updated the firmware on library , clean up a tape for test , and in a few days we will see if that fix the issue

  • mph999's avatar
    mph999
    Level 6
    2 years ago

    There are no settings in NetBackup that control tape capacity

    NetBackup passes data to the OS, one block at a time, to be written to the tape drive. NetBackup has no concept of tape capacity. In theory, it would keep writing to the same tape "forever".

    The tape drive firmware detects when the tape physically passes the logical end-of-tape, which is a marker written to the tape during manufacture. It then sets a 'flag' in the tape driver. There is still enough physical space on the tape for the current block to be written, so this completes successfully. NetBackup then tries to send the next block of data but the tape driver refuses, as the 'tape full' flag is set. The driver passes this 'tape full' message to the OS, which then passes it to NetBackup. This causes NetBackup to mark the tape as full, and load a new one.

    Common causes of this issue are tape drive firmware, or faulty hardware, or possibly a driver issue.

    • davidmoline's avatar
      davidmoline
      Level 6
      2 years ago

      Hi solomοn 

      The other thing to consider, most (all?) modern tape drives will comrpess data by default. The drive capacity is typically given as twice the raw capacity of the drive. Given you have created a new pool, presumably this is for different backups that may not compress the same as you have previously achieved.

      Cheers

  • mph999's avatar
    mph999
    Level 6
    2 years ago

    David makes a good point.

    Tapes have 2 capacities, uncompressed (native) and compressed.
    For example, an LTO 8 tape holds 12 TB uncompressed, and about 30 TB compressed.
    If you write un-compressible files to the tape, for example .jpeg or files that are already zipped, the tape will become full at 12TB.  If you write compressible files for example .txt files, you will fit more than 12TB of files on the tape (how much more depends on how compressible the files are).

    So a person may think the tape is becoming full early, but in fact it's just that the data being written cannot be compressed as well as expected.

    If the amount of data on a tape when it becomes full, is less that the uncompressed capacity, then in that instance you know for certain there is a problem.  A tape should always be able to hold it's uncompressed capacity.

  • Mxyda's avatar
    Mxyda
    Level 1
    2 years ago

    good explanation , thanks for the info guys ,

    i updated the firmware on library , clean up a tape for test , and in a few days we will see if that fix the issue