Hi John: The cost for extra extents occurs when the extent is required because of thbe overhead of having to go to the catalog and VTOC. There is a little more virtual storage required. The only other danger is that you run out of available extents allowed for the component.
Regards, Gene Sent via BlackBerry by AT&T -----Original Message----- From: "McKown, John" <[EMAIL PROTECTED]> Date: Thu, 26 Jul 2007 11:06:36 To:IBM-MAIN@BAMA.UA.EDU Subject: VSAM in extents I'm curious about this one. A person here has stated that when a VSAM KSDS file is in multiple extents, it performs more poorly than it would in a single contigueous extent. He said something to the effect that when a portion of the index is referenced which is in "another extent" that the entire in-memory buffer for the file is flushed. I have no idea where he got this information. Also, he wants to use SMS striping for VSAM files which are mainly accessed sequentially because it would significantly decrease the I/O time to read. We are using multiple FICON connections to a single 2105 ESS (Shark). We do not have the volumes in any storage group spread across LCUs. My contention is that it may well decrease I/O, but it would require that we likewise stripe the volumes across the 2105's LCUs as well. We don't do this at present. -- John McKown Senior Systems Programmer HealthMarkets Keeping the Promise of Affordable Coverage Administrative Services Group Information Technology The information contained in this e-mail message may be privileged and/or confidential. It is for intended addressee(s) only. If you are not the intended recipient, you are hereby notified that any disclosure, reproduction, distribution or other use of this communication is strictly prohibited and could, in certain circumstances, be a criminal offense. If you have received this e-mail in error, please notify the sender by reply and delete this message without copying or disclosing it. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
