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Turning off Compression

Lon Anderson
Occasional Visitor

Turning off Compression

I have a Dat40 (C5683A) drive. I regularly back data that is already compressed. My software compression is off but I can't find any switches to turn off the hardware compression. I generally get requested for a new tape near 12.7 GB on a 20-40 gig tape. Is there a script or something to change the hardware compression?
7 REPLIES
Leif Halvarsson_2
Honored Contributor

Re: Turning off Compression

Hi
Which OS is on the computer the drive is connected to. If Unix the best way to turn off compression is to create a uncompressed device file.
Ted Ellis_2
Honored Contributor

Re: Turning off Compression

this link has some great info:

http://forums.itrc.hp.com/cm/QuestionAnswer/0,,0xb36737f45ef7d4118fef0090279cd0f9,00.html

your device file will determine of you are using hardware compression, and the /dev/rmt/xm device files are often linked to the device files with names like /dev/rmt/cctxdxBEST (these are hardware compress device files)

here is a little plagarism:

You will obtain the most-for-the-money by using the 'BEST' device files. Normally these are already linked to '/dev/rmt/?m'. You can verify that you are using the best density (compression) by comparing the minor numbers of the device files for "?m" with "c?t?d?BEST" and noting identical values. For example, 0x030000 for /dev/rmt/0m as well as for /dev/rmt/c3t0d0BEST would denote equivalent devices. You can also verify that compression is available by doing an 'lssf ', as for instance, 'lssf /dev/rmt/0m'.

further into that link you will see some steps to reset the device files so they are not linked to compression.

Ted
Lon Anderson
Occasional Visitor

Re: Turning off Compression

I should have been a little more clear. It is on a WindowsXP box. I cannot find any info on the DIP switch settings. TapeTools reports that hardware compression is enabled. I don't know how without any documentation on the DIP switches or if anything can be done in windowsXP. This is on an Adaptec 39160 SCSI card. Thanks
Leif Halvarsson_2
Honored Contributor

Re: Turning off Compression

Hi
Is there no option in your backup software for hardware compression on/off.
Leif Halvarsson_2
Honored Contributor

Re: Turning off Compression

Hi

I found this document about switch settings. I am not sure if it is relevant for your drive but you can try.

http://www.hp.com/cposupport/information_storage/support_doc/lpg51068.html
Lon Anderson
Occasional Visitor

Re: Turning off Compression

Leif,

I found a similar document for another HP tapedrive. The switch settings are the same in both documents.

I just changed them and checked it. TapeTools that now reports "Compression is OFF" Thank you. I was skeptical about changing them without some corroboration!!
Marino Meloni_1
Honored Contributor

Re: Turning off Compression

hi,
have a look at this link, you will found lots of informations about conpression on DDS products

http://bizforums.itrc.hp.com/cm/QuestionAnswer/1,,0xc30e36e69499d611abdb0090277a778c,00.html