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List:       amanda-users
Subject:    Re: Tape Compression: Is it on or off?
From:       Jon LaBadie <jon () jgcomp ! com>
Date:       2013-10-17 6:00:47
Message-ID: 20131017060047.GA11038 () cyber ! jgcomp ! com
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On Thu, Oct 17, 2013 at 11:19:44AM +1100, Tom Robinson wrote:
> On 16/10/13 15:53, Jon LaBadie wrote:
> > On Wed, Oct 16, 2013 at 11:15:41AM +1100, Tom Robinson wrote:
> >> Hi Paul,
> >>
> >> Thanks for your detail explanation. It is good to have confidence that amtapetype is reporting the
> >> compression setting correctly. It gives me no confidence in my ability to follow logic.
> >>
> > ...
> >> Also, the native speed of LTO5 is stated as 140MB/s. If I do manage to turn compression off, is it
> >> at all likely that I will achieve anyway close to that speed? You can see that with a 2MB block I am
> >> getting about 86MB/s.
> >>
> > The list has many reports of difficulty getting the theoretical maximum
> > speeds of LTO drives.  Those that succeed typically have scsi
> > controllers with rated speeds well above the tape drive.  And they
> > deicate the controller to the single device to prevent bus contention.
> >
> I have the tape unit passed through the backplane expanders where there are also five disks (for ARC
> and ZIL caches). This probably accounts for some loss of speed. Is there any concern that tape and
> disk operations will interfere with each other? Should I invest in a dedicated card for the tape unit?

That is a question best answered by you after you've had some
experience with your amanda installation.  Keep it available
as an option if you find you need faster taping.  If your
tapetime is 26 hrs, you obviously will need to do something.
If your run last 6 hrs and the taping part is only 2 hrs,
what will you gain by speeding up taping?

Amanda reports can give you a lot of information to ask and
answer these questions, but only after it has been running
a bit.

Jon
-- 
Jon H. LaBadie                 jon@jgcomp.com
 11226 South Shore Rd.          (703) 787-0688 (H)
 Reston, VA  20190              (609) 477-8330 (C)
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