Veritas-bu

[Veritas-bu] Implications of turning off s/w compresion?

2002-04-02 10:02:14
Subject: [Veritas-bu] Implications of turning off s/w compresion?
From: jlkennedy AT amcc DOT com (Jeff Kennedy)
Date: Tue, 02 Apr 2002 07:02:14 -0800
"Richard.Hall" wrote:
> 
> Recent discussion here has convinced me that we should never have set up
> NBU s/w compression in the first place. ("Told you so"!!)

If you're backing up over a LAN (or even a high-speed WAN, just not a
modem....) there are *very* few reasons to enable sw compression.

> 
> Before we turn it off ...
> 
> 1) will this affect recovery from existing images?

No, at least it's not supposed to.

> 
> 2) or mess anything else up?

Nope.

> 
> 3) (For academic interest only, and to make sure I understand what is
>    going on)
>    Since our DLT7000s are currently managing ~5Mb/sec, I assume that the
>    data is currently compressed on the client side, not decompressed again
>    on the server side, and the drives are (roughly) achieving no further
>    compression. And that, other things being equal, I can now expect to
>    see them managing 10 Mb/sec, but with no reduction in backup time.
>    Except perhaps in the tail of the backups, where the number of jobs and
>    the total data rate is falling.

Maybe not double, but definitely more.  I don't run compression and my
DLT7k's generally run at 8-10MB/sec, but with hw compression that put's
me at approx. 4-5MB/sec compressed, which is what they should be running
at.  Occasionally I see my filers pushing them to 14MB/sec but those are
burst speeds.  And in fact, backup jobs may run noticeably faster if the
clients were cpu constrained to begin with.  Not having to do
compression will lighten cpu load tremendously.

~JK
-- 
=====================
Jeff Kennedy
Unix Administrator
AMCC
jlkennedy AT amcc DOT com

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