Results 1 to 5 of 5

Thread: Hardware Compression Confusion

  1. #1

    Default Hardware Compression Confusion

    I am running 2.4.5 on Core 4.
    I have enabled compression on my HP DDS-4 autoloader. That should give me about 40G per tape. When I try to backup, it fails with this message -
    lev 1 FAILED [dump larger than tape, 18398347 KB, skipping incremental.

    Running amtapetype w/compression reports:
    define tapetype unknown-tapetype {
    comment "just produced by tapetype prog (hardware compression on)"
    length 17000 mbytes
    filemark 403 kbytes
    speed 1587 kps
    }


    Running amtapetype without compression:

    define tapetype HP-C5713A {
    comment "just produced by tapetype program"
    length 17021 mbytes
    filemark 403 kbytes
    speed 1587 kps
    }

    I know I'm missing something. Should I change the length to 40000?

    Thanks,
    Steve
    Last edited by steves; August 1st, 2006 at 10:15 AM.

  2. #2
    Join Date
    Sep 2006
    Posts
    29

    Question Does Amanda require hardware compression to be off?

    I too am confused about Amanda and compression.

    I ran amtapetype with compression on.

    I saw the [URL="http://wiki.zmanda.com/index.php/Tapetype_definitions#DDS-2_120_meter_tapes"]comment[/URL]
    "Running amtapetype on your installation instead of just using the values found here, allows you to verify the capacity (is hardware compression "on" by mistake?) and speed (is there a problem with my SCSI chain?)."

    Hardware compression should be off? amtapetype and tapetype definition should be with compression off?

    This must be documented some place , but I either missed it or haven't found it yet.

    Any pointers would greatly be appreciated.

    Thank you.

  3. #3
    Join Date
    Oct 2005
    Posts
    1,559

    Default

    It is upto to the user to decide whether they want to use hardware
    compression or not.

    If you are planning to use hardware compression, run amtapetype
    with hardware compression on. Otherwise, don't leave hardware
    compression on when you run amtapetype.

    amtapetype uses random data to estimate the size of media. If hardware
    compression is turned on, the amtapetype results will not match
    the actual results. It is nearly impossible to determine the media
    size when hardware compression is on because the compression
    depends on the data.

    Amanda's software compression will work better because it can be
    done on either Amanda server or client. Software compression can
    be specified for some DLEs in a backup run. So, data that is already
    compressed such as images can be configured for "no compression".

    Paddy

  4. #4

    Default Follow up question about amtapetype

    Quote Originally Posted by paddy
    <snip>
    If you are planning to use hardware compression, run amtapetype
    with hardware compression on. Otherwise, don't leave hardware
    compression on when you run amtapetype.
    <snip>
    <snip>
    Paddy
    Perhaps this should be obvious but rather than overlook it and regret the results...

    I have an Exabyte VXA-2 1x10 1U w/X10 tapes.

    Running amtapetype wo/compression and an estimated size of 40GB yields:

    define tapetype X10 {
    comment "Exabyte VXA-2 X10"
    length 40759 mbytes
    filemark 2172 kbytes
    speed 6024 kps
    }

    ...running w/compression yields:

    define tapetype X10c {
    comment "just produced by tapetype prog (hardware compression on)"
    length 36044 mbytes
    filemark 0 kbytes
    speed 5380 kps
    }

    Here's where things get muddy; should I specify 40GB as the estimated size presuming an 80GB result with hw compression turned on, or should I specify 80GB as the estimated size? If I recall correctly, I specified an estimated size of 40GB for X10c.

    TIA

  5. #5
    Join Date
    Oct 2005
    Posts
    1,559

    Default

    Use the tapetype obtained with estimated size as 40GB (no compression). The actual compression acheived depends on the data being written.

    Amanda uses tapetype definition length parameter only in the estimation phase to do backup planning for the run. When it writes to the media, it continues to write till it gets an error.

    Paddy

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •