David, The Iceberg's sequential pre-fetch performance was not one of its finest moments. If you are seeing disconnect time of 10ms or more for your sequential IO then restricting your work to 8 stripes may not be the best thing for your workload. A larger number of stripes and corresponding BUFNO changes would increase the IO transfer and cache miss overlap.
Disconnect time for sequential IO means that channels are not the choke point. Ron > -----Original Message----- > From: IBM Mainframe Discussion List [mailto:[EMAIL PROTECTED] On > Behalf Of David Andrews > Sent: Tuesday, April 08, 2008 6:19 AM > To: [email protected] > Subject: Re: [IBM-MAIN] Sequential Data Striping > > On Tue, 2008-04-08 at 09:38 +0800, Jason To wrote: > > David, how did you code your ACS routine to select different storage > > classes? Can you send me a sample? TIA. > > Rather than mail it to you I'll post it. Maybe someone else will see > something *I've* done wrong. > > Our DC routine assigns a DATACLAS of 'SMSEXT' if we want the dataset to > be system-managed and extended-format (pretty much the default > condition), and 'SMSCOMP' if we additionally want the dataset to be > compressed (assigned on a special case basis). > > The SC routine selects a storage class based on the DATACLAS name and > the dataset's &SIZE. Here's an extract: > > FILTLIST EXTCLASS INCLUDE('SMSCOMP','SMSEXT') > > /* > * IF THE DATA CLASS IS EXTENDED FORMAT, THEN CHOOSE > * A STORAGE CLASS BASED ON THE DATASET SIZE. > * > * THE EXTENDED FORMAT STORAGE CLASSES DIFFER FROM EACH > * OTHER ONLY BY THEIR "SUSTAINED DATA RATE" SPECIFICATIONS. > * THESE ARE WHAT DRIVE THE SMS STRIPING DECISION -- YOU > * GET ONE STRIPE FOR EVERY 4MB/SEC. > */ > > IF (&DATACLAS = &EXTCLASS) && (&DSORG = 'PS') THEN DO > SELECT > WHEN (&SIZE > 256MB) SET &STORCLAS = 'STRIPED8' > WHEN (&SIZE > 128MB) SET &STORCLAS = 'STRIPED4' > WHEN (&SIZE > 64MB) SET &STORCLAS = 'STRIPED2' > OTHERWISE SET &STORCLAS = 'MANAGED' > END > EXIT > END > > The STRIPED(2/4/8) storage classes are defined with SUSTAINED DATA > RATES > of 8/16/32. > > The number of stripes I assign versus the dataset size was arbitrary. > I > have eight ESCON paths to my Iceberg, so that's the max stripe count I > ever set. > > -- > David Andrews > A. Duda and Sons, Inc. > [EMAIL PROTECTED] > > ---------------------------------------------------------------------- > 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
