John, For your first paragraph, lets just put it with all those other extent myths. I mean, for sequential access you're just reading the sequence set anyway - what is there to flush!!!
Striping sequential datasets can definitely speed up sequential access, but you may need to experiment with the BUFND number that gives you the best results for the combination of stripes and CISZ you use. There is no need to spread stripes across LCU or LSS. It would be more important to spread the STORGRUP evenly across the Bays, Parity Groups and Cache-Halves to give ESS the best chance of pre-fetching from disk faster than the channels request it. Ron > -----Original Message----- > From: IBM Mainframe Discussion List [mailto:[EMAIL PROTECTED] On > Behalf Of McKown, John > Sent: Thursday, July 26, 2007 9:07 AM > To: IBM-MAIN@BAMA.UA.EDU > Subject: [IBM-MAIN] 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 > ---------------------------------------------------------------------- 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
