Re: tape compression on hardware and compression via device ( /dev/rmt/1[m,c]n )
From: Darren Dunham (ddunham_at_redwood.taos.com)
Date: 06/30/05
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Date: Thu, 30 Jun 2005 16:05:59 GMT
jms <noone@noone.org> wrote:
> Is there a relationship between the tape compression on the hardware and
> usage of the compression level on the tape device ( e.g. /dev/rmt/1mn
> or /dev/rmt/1cn ).
Depending on the specifics of the hardware, yes.
> Does using the compression on the tape device enable ( or disables in the
> absence of the compression level on the device ) the compression on the
> hardware ? ( via the driver that somehow tells the hardware to use / not
> use compression ) ?
Yes. The 'st' driver has some built-in settings for tapes, and can also
read entries in /kernel/drv/st.conf. There are two ways of dealing with
compression, depending on the specifics of the drive.
In *most* cases where compression is available, writes to the correct
device will select the correct compression on the fly (it's not usually
limited to one setting across the entire tape like the density is).
-- Darren Dunham ddunham@taos.com Senior Technical Consultant TAOS http://www.taos.com/ Got some Dr Pepper? San Francisco, CA bay area < This line left intentionally blank to confuse you. >
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