no compression using seagate scorpian dss-4 drive

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no compression using seagate scorpian dss-4 drive

Christopher Mosentine
Hello:  I am using bacula with my seagate scorpian dss-4 drive.  I
love how bacula has support for my tape drive right out-of-the-box.

Bacula is running fine but I am not able to achive any compression as
I am only able to put about 17GB on a tape.  I routinely backup about
32GB and would love to get it all on 1 tape.  I used to use Arkeia but
achived the same results.  I have checked and the device IS set with
hardware compression ENABLED (via dip switch).

So, I know there are others out there using this same drive - have you
been able to get hardware compression to work??  If so how??

Thanks, Chris.


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Re: no compression using seagate scorpian dss-4 drive

Arno Lehmann
Hello,

Christopher Mosentine wrote:

> Hello:  I am using bacula with my seagate scorpian dss-4 drive.  I
> love how bacula has support for my tape drive right out-of-the-box.
>
> Bacula is running fine but I am not able to achive any compression as
> I am only able to put about 17GB on a tape.  I routinely backup about
> 32GB and would love to get it all on 1 tape.  I used to use Arkeia but
> achived the same results.  I have checked and the device IS set with
> hardware compression ENABLED (via dip switch).
>
> So, I know there are others out there using this same drive - have you
> been able to get hardware compression to work??  If so how??

Have you tried checking if compression is enabled using mt or tapeinfo?
Then, you can verify the actual tape capacity using random data and dd.

To my knowledge, DDS-4 is 20GB uncompressed, so, assuming not further
compressible data 17GB is not unrealistic, considering the 10^3 vs. 2^10
differences...

Arno

> Thanks, Chris.
>
>
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Re: no compression using seagate scorpian dss-4 drive

C M Reinehr
In reply to this post by Christopher Mosentine
On Monday 30 May 2005 02:25 pm, Christopher Mosentine wrote:

> Hello:  I am using bacula with my seagate scorpian dss-4 drive.  I
> love how bacula has support for my tape drive right out-of-the-box.
>
> Bacula is running fine but I am not able to achive any compression as
> I am only able to put about 17GB on a tape.  I routinely backup about
> 32GB and would love to get it all on 1 tape.  I used to use Arkeia but
> achived the same results.  I have checked and the device IS set with
> hardware compression ENABLED (via dip switch).
>
> So, I know there are others out there using this same drive - have you
> been able to get hardware compression to work??  If so how??
>
> Thanks, Chris.

Chris,

I'm using a Certance DDS-4/DAT72 drive, which I believe is the same as yours,
perhaps just a later model since all Seagate tape drives now are Certance. As
you said, data compression is set with a DIP switch. Here's the output of
tapeinfo -f /dev/sg0:

Product Type: Tape Drive
Vendor ID: 'SEAGATE '
Product ID: 'DAT    DAT72-000'
Revision: 'A030'
Attached Changer: No
SerialNumber: 'HV00D4Z'
MinBlock:1
MaxBlock:16777215
SCSI ID: 6
SCSI LUN: 0
Ready: yes
BufferedMode: yes
Medium Type: 0x35
Density Code: 0x47
BlockSize: 0
DataCompEnabled: yes
DataCompCapable: yes
DataDeCompEnabled: yes
CompType: 0x20
DeCompType: 0x20
BOP: yes
Block Position: 0

which clearly shows data compression enabled and I routinely get something on
the order of 60GB's of data per tape.

HTH's!

cmr

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