Reza,
It's LZW compression which has an asymmetric cost by design - compressing
always costs more than decompressing.
Back when the compression assist instructions were announced IBM were saying
the difference was around 6:1 compression vs decompression.
The compression and compression and decompression costs will depend on how
you use your dictionaries.
Personally I've found two killer apps for DFSMSdfp compression:
1) Large datasets updated/created in the batch critical path when
using Synchronous Remote Copy.
2) Large datasets that are read over and over again after they are
created (backups, reporting, DW extract, etc)
Ron
> -----Original Message-----
> From: IBM Mainframe Discussion List [mailto:[email protected]] On
Behalf Of
> R Hey
> Sent: Tuesday, February 16, 2010 5:04 PM
> To: [email protected]
> Subject: [IBM-MAIN] SMS compression cost & size
>
> Hi,
>
> Are there any figures for the cost of SMS compression out there,
> or is it YMMV?
>
> (I've checked the archive to find cost is higher for W than for R ...,
> seen many who decided not to do it with a lot of YMMV ...)
>
> Also, are there any ROT for the min size to compress for?
>
> One client I had compressed data if it was > 5 Cyl !
> This doesn't make sense to me.
>
> What's the min size you use for compress.
>
> Book says:
>
> Compress when an existing data set is approaching the 4 gigabyte VSAM size
> limit or when you have capacity constraints
>
> The data set must have a primary allocation of at least 5 MBs, or 8 MBs if
no
> secondary allocation is specified.
>
> TIA,
> Rez
>
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