1. DB2 tries very hard to minimize the size of the extent defined in the Define Extent CCW for each I/O that it does to a Shark-type DASD that supports Multiple Allegiance (MA). E.g., if an I/O references only one track, then that channel program will have only that one track within the defined extent. To verify, run GTF and trace I/Os to that one volume from DB2, then look at the defined extents that will appear in the Prefix CCW for SSCH trace records and in the Define Extent for I/O interrupt trace records.
2. I don't know for sure, but I imagine that WLM will allow the device to have as many PAVs as its controller microcode support. E.g, for the 2105s available in 2000 when I last looked at this issue, the maximum number of simultaneous I/Os allowed by the microcode to any one device was eight regardless of how many PAVs were assigned. Eight was the maximum MA level. The number of PAVs can be less than, equal to, or greater than the max MA number, but any more than the max will result in queued I/O requests if the workload produces simultaneous I/Os fast enough. Bill Fairchild Software Developer Rocket Software 275 Grove Street · Newton, MA 02466-2272 · USA Tel: +1.617.614.4503 · Mobile: +1.508.341.1715 Email: [email protected] Web: www.rocketsoftware.com -----Original Message----- From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf Of Terry Draper Sent: Tuesday, November 24, 2009 2:32 AM To: [email protected] Subject: DB2 and PAV 1. The DASD controller will serialise writes to the same extent - as specified in the define extent CCW. What does DB2 specify for the extent? Is the the DASD extent or just the area it is writing to? If so what area is specified? I cannot find this documented anywhere. The many write engines will be trying to build the single table. 2. We may have many write engines started to the same DB2 table on a single volume. There may be many of these.What is the maximum number of PAVs that WLM will give it? Terry Draper zSeries Performance Consultant ---------------------------------------------------------------------- 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
