Gene, I have not heard of a CA being "cleared out." My old notes say that all CI with a key higher than the mid-point sequence set record are written to the new CA. The space in the old CA is now marked free - it is not formatted.
If you are using CA of 1 CYL then it is unlikely to upset the pre-fetch algorithm in most storage. The sequence set within a CA are in order and with default buffering (BUFND=2) or SEQ bias (half CYL) you will get sequential cache hits. That assumes that your disk vendor recognizes the Seq bit. This is not the case for all vendors. A heavily fragmented KSDS may not have pre-fetch detected with a large BUFND because it jumps out of the monitored area before enough seq IO takes place. It is likely that the CI split that instigated the CA split will be a DFW hit because the old tracks are still in cache - but that's a nit. Ron BTW my notes make a post of mine about the duration of CA splits wrong. It is only halve IO cost I estimated. I should have check first. Where's my "Ronald K. Ferguson" bible when I need it? > -----Original Message----- > From: IBM Mainframe Discussion List [mailto:[EMAIL PROTECTED] On > Behalf Of Gene Hudders > Sent: Wednesday, February 20, 2008 1:02 PM > To: [email protected] > Subject: [IBM-MAIN] Questions Regarding Disk Cache > > Hi: > > These were a few questions posted on another topic in CICS-L for which > no > reply was received. The topic was CI/CA splits and I asked the > following > questions, which were embedded in the response: > > 1) Two of the processes of completing a CA split is to format the new > CA and > clear out the moved data CIs from the original CA. Do the "empty" CIs > used > to clear or format the CAs occupy space in the disk cache? > 2) When reading a file sequentially that has CA splits caused by direct > insertions (e.g., 50% free space), are the empty CIs that were created > as a > result of the CA splits read into the disk cache by the hardware's > read-ahead > mechanism once it determines that the file is being processed > sequentially? > > Regards, > Gene > > > > > > > **************Ideas to please picky eaters. Watch video on AOL Living. > (http://living.aol.com/video/how-to-please-your-picky-eater/rachel- > campos-duffy/ > 2050827?NCID=aolcmp00300000002598) > > ---------------------------------------------------------------------- > 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
