Re: DDS3 Tape drive not compressing?

From: Alan D Johnson (adjtech_at_hvc.rr.com)
Date: 10/24/05

  • Next message: Manoj R: "Re: Kernel threads on HP-UX" 
    Date: Mon, 24 Oct 2005 21:54:22 GMT

    Alan D Johnson wrote:

    > Frank Slootweg wrote:
    >
    >> Adam Skeggs <fun@optusnet.com.au> wrote:
    >>
    >>> Hi,
    >>>
    >>> I have a HPUX 11.11 box with a C1537A tape drive which is I believe
    >>> DDSIII. Trouble is I can't see that hardware compresssion is working.
    >>
    >>
    >>
    >> Check the drive's hardware settings to see if it is not set to no
    >> compression. Most drives can be set to compression, no compression and
    >> software controlled (non) compression.
    >>
    >>
    >>> Using omniback the media look like DDSIII as the capacity is about 12Gb:
    >>> $omnimm -media_info 581490 -detail
    >>> ...
    >>> Total blocks : 11743616
    >>> (or is this the compressed capacity being reported? No that doesn't
    >>> make much sense)
    >>
    >>
    >>
    >> It indeed reports the uncompressed capacity.
    >>
    >>
    >>> Trouble is when I write 12Gb (added up totals from bdf) it's too much
    >>> - thus there is no compression going on it seems.
    >>
    >>
    >>
    >> bdf info is rather meaningless, because it does not account for the
    >> OmniBack 'overhead'.
    >>
    >> Try to create a datalist/backup_specification which would result in a
    >> *little* more written to the drive, preferably some 13GB. As soon as you
    >> can write more than 12GB, you *know* that hardware compression is
    >> working, because the Native Mode (is uncompressed) capacity of DDS-3 is
    >> 12GB, i.e. anything above 12GB is compressing.
    >>
    >> Also make sure that you do *not* specify compression in OmniBack. In
    >> OmniBack, "compression" is *software* compression and software
    >> compression can/will conflict with hardware compression. I.e. if both
    >> are enabled, you will only be able to write *less* than 12GB
    >> (uncompressed), instead of more.
    >>
    >>
    >>> I am using the compression device: /dev/rmt/c1t0d0BEST which should
    >>> be the right one.
    >>
    >>
    >>
    >> Make sure that lssf(1M) actually says "best density".
    >>
    >>
    >>> So I am a bit stumped.
    >>>
    >>> Any clues?
    >>> Thanks,
    >>> Adam.
    >>
    >>
    >>
    >> If all the above does not help, you could try the ddsinfo utility from
    >> "The Porting and Archive Centre for HP-UX" <http://hpux.connect.org.uk>.
    >> It is rather old and had some limitations. I don't now if there is
    >> anything newer/better somewhere.
    >
    > There is also the StorageWorks Library and Tape tools, the Windows
    > versions works OK, I've never used the HPUX one. A quick search on ITRC
    > did not find it, what a surprise...
    Oops, helps if I speel rite..
      http://h18006.www1.hp.com/products/storageworks/ltt/index.html

  • Next message: Manoj R: "Re: Kernel threads on HP-UX"

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