We found using both DFSMS compression and striping or Innovation IAM
compression that in most cases we gain significantly in performance and
save DASD as a side benefit with compression. The CPU increase to write
the data was more than offset by the performance gains and only moderate
increase in CPU to read the data.
Best Regards,
Sam Knutson, GEICO
System z Performance and Availability
mailto:[EMAIL PROTECTED]
(office) 301.986.3574
"Think big, act bold, start simple, grow fast..."
-----Original Message-----
From: IBM Mainframe Discussion List [mailto:[EMAIL PROTECTED] On
Behalf Of John Kington
Sent: Wednesday, November 14, 2007 8:10 AM
To: [email protected]
Subject: Re: SMS Advanced Feature
Jason,
> We are planning to implement SMS data compression. I've read that we
> cannot implement compression on VSAM file that is open for update. Is
> this true? Aside from this, any other considerations?
>
Compression will not take place until you recreate the vsam dataset. The
danger with updating a compressed vsam dataset is that you will likely
change the size of the data and an increase could cause you to incur
a CI split. Otherwise you can compress a vsam dataset that is updated.
We looked at using compression but determined that CPU costs exceeded
what we saved in dasd costs. Your mileage may vary.
Regards,
John
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