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List:       adsm-l
Subject:    Re: Antwort: Re: low bandwitdth and big files
From:       "Slag, Jerry B." <jslag () STATE ! ND ! US>
Date:       2002-01-31 20:25:03
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1. Hardware microcode is smart - software can be stupid. Using "compression
yes" and /or "compressalways yes" can and will cause some files to increase
in size.
2. We have compression turned on within the 3494, within our ZOS operating
system and within System Managed Storage settings. If any of these are on it
does not matter what TSM tries to do - these settings override. Obviously if
you do not have anything controlling compression at a higher level TSM may.
I believe the hardware default for 3590 drives is to have compression on.

-----Original Message-----
From: Nicholas Cassimatis [mailto:nickpc@US.IBM.COM]
Sent: Thursday, January 31, 2002 1:42 PM
To: ADSM-L@VM.MARIST.EDU
Subject: Re: Antwort: Re: low bandwitdth and big files


1. Am I potentially doubling the size of certain files in the stg pool by
running multiple compression algorithms.?

No - the drive logic won't compress already compressed data, so there's no
real risk of this.

2. By turning off DEVCLASS compression, is that effectively disabling
hardware compression performed by my tape device (IBM 3590 TAPE Device /
Cartridge)

Yes.

3. If client compression and hardware compression are turned on, and
hardware compression isn't really buying me anything... won't the attempt
at hardware compression prevent streaming?  I think it
will.

Nope, not to the best of my knowledge.  In fact, a pre-compressed data
stream is less likely to starve the drive.

I'm looking for YES/NO answers with a valid explanation.  Anyone?????


Nick Cassimatis
nickpc@us.ibm.com

Today is the tomorrow of yesterday.

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