Networker

Re: [Networker] tape drive hardware compression a bad thing?

2003-01-29 10:14:43
Subject: Re: [Networker] tape drive hardware compression a bad thing?
From: Davina Treiber <treiber AT HOTPOP DOT COM>
To: NETWORKER AT LISTMAIL.TEMPLE DOT EDU
Date: Wed, 29 Jan 2003 10:14:46 -0500
On Wed, 29 Jan 2003 08:18:25 -0500, Jim Lane <JLane AT TORONTOHYDRO DOT COM> 
wrote:

>I recently had a contractor/consultant onsite to review my Networker
>setup. among other things he insisted that using hardware compression on
>a tape library is a "bad thing". the closest thing to an explanation I
>ever heard was that it might cause data loss somehow and that Legato
>wouldn't help me if it did.
Sounds to me like the consultant is trying to come up with some conclusions
to justify his existence. This information is of course nonsense. The
hardware compression is handled by the tape firmware and has worked
perfectly. There is no possibility that hardware compression would cause
data loss.

> since contractors have a better relationship
>with management than I do
I wouldn't like to be in your career position. If I was you I think I'd be
looking for a new job where I could get some appreciation and skills
recognition.

> he just called STK onsite and had them turn
>compression off on my 9710.
So how could they do that? Usually the compression is selected by the choice
of tape device (e.g. cbn on Solaris).I suppose you could perhaps override
this on the tape drive, but I wouldn't advise it. Your management have been
hoodwinked, not only have they paid for bad advice from a consultant, it is
also going to cost them about twice as much for extra media, and possibly
more for the new tape libraries to accommodate the extra media. People like
this give consultants a bad name.

> I'm wondering if anybody out there has ever
>heard anything like this before? does anybody have any experience of the
>possible effects, on either reliability or performance, of tape hardware
>compression?
The only thing I know of that is similar to this is tape buffering in
Solaris. This is controlled by a flag in st.conf, and the theory is that
data may be lost during tape spanning if this is turned on. These days with
up to data st patches it is not necessary to even configure settings for
well known devices such as DLT7000, so defaults are normally used, even if
it includes the tape buffering setting, and I have not heard any cases of
data loss.

Hope this helps.

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