Re: DDS3 Tape drive not compressing?

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

Date: Mon, 24 Oct 2005 21:50:58 GMT

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...

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