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Thread: Low hardware compression rate (LTO-4)

  1. #1
    Join Date
    Apr 2013
    Posts
    2

    Default Low hardware compression rate (LTO-4)

    Hi,

    I'm using a TANDBERG LTO-4 HH device with 800/1600Gb tapes.
    I would like to use only hardware compression in my backup process, because software take too much time.

    First of all, I need to determinate the compression rate of my tape, but i'm stuck.

    Here the test i've tried:

    Append "/etc/stinit.def" with
    Code:
    manufacturer=TANDBERG model = "LTO-4 HH" {
    mode1 blocksize=256 compression=1
    }
    After that, I wrote on the tape as follow:
    # stinit
    # mt-f /dev/nst0 tell (to get the start block number)
    # tar cf /dev/nst0 file (file is a 800Mb text-file, so highly compressible)
    # mt-f /dev/nst0 tell (to get the last block)
    Then, i do : (last block number - start block number)*256 to get the size of file on the tape.
    The figure 256 is the block size specified in stinit.def.

    The is result is: 798Mb.

    So, i conclude that my tape hasn't compressed anything, and i can't see why.

    I've also tried to check if the compression was enabled with Amanda tool's amtapetype, heres the output:

    [HTML]# amtapetype -cf DailySet1 /dev/nst0[/HTML]
    Code:
    Checking for FSF_AFTER_FILEMARK requirement
    Applying heuristic check for compression.
    Wrote random (uncompressible) data at 43360121.704918 bytes/sec
    Wrote fixed (compressible) data at 53978927.0204082 bytes/sec
    Compression: enabled
    So, I've configured my scsi drive to enable hardware compression, Amanda says it's on, but yet my tape won't compress datas. How come ?

    Thank you for your help.
    Last edited by Skiny13; April 17th, 2013 at 05:10 AM.

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