Several authoritative sources tell me that hardware compresssion does NOT expand
already compressed files. Though software compression (as on the *SM client)
very likely WILL increase the size of, say, a gzip file, compression on the tape
drive itself will NOT.
Hope this helps.
Gary Ison wrote:
> Bill,
>
> Compression is, obviously, very dependent on data type. I have
> achieved up to 80% compression on database dumps (Sybase) with large amounts
> of blank space. Compression of already compressed files can result in
> backup failures unless you use the "compressalways=yes" option because
> compression may actually increase the files' size. It will reduce the
> network volume, but it can be client CPU intensive to compress the data and
> may result in somewhat slower backup speeds. I have heard reports that
> decompression is more efficient than compression, but haven't tried to
> verify them. There is also the issue of hardware compression on tape
> volumes - the same as compressing a compressed file; it may grow.
>
> Most of my clients do compression because we bill them for our TSM
> service based on the amount of data transferred. Compression gives them
> some relief when paying their bill.
>
> Gary L. Ison
> Governor's Office for Technology
> 101 Cold Harbor Drive
> Frankfort, Ky. 40601
> Phone: (502) 564-8724
> Fax: (502) 564-6856
> E-mail: Gary.Ison AT mail.state.ky DOT us <mailto:Gary.Ison AT mail.state.ky
> DOT us>
>
> -----Original Message-----
> From: Bill Sherrill [SMTP:billsh AT US.IBM DOT COM]
> Sent: Wednesday, May 10, 2000 10:23 AM
> To: ADSM-L AT VM.MARIST DOT EDU
> Subject: Client Compression
>
> Does anyone have any numbers for Client Side compression? Because of
> network throughput, we are looking at setting compression on the client.
>
> Thanks,
> Bill Sherrill
> Analyst International Corp.
--
Mr. Lindsay Morris
Mr. Lindsay Morris
Certified: AIX,ADSM, TSM, HACMP,SP
Gresham Enterprise Storage
lmorris AT openmic DOT com
606-253-8000
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