Lizette (OP),
I would not recommend going to 32K as a blocking factor. Generically speaking, all three vendor emulate a CKD track, allocating up to 64KiB of space for every track. Whether you use a regular formatted volume, or thin provisioning (DP-VOL in Hitachi speak), if you write a 32K block to an emulated 3390 track, the balance of the space will be wasted. Ipso fact you will use 41% more space for the same amount of data at half-track. 1-(32768/(27998*2))=41% Performance wise you will see almost no difference between a half track and 32K block IO. The normal defaults and limits for BAM chain length will apply so you may pick up a few more bytes with the default of 5 buffers and 32K blocks, but without zHPF there will be no benefit with a BUFNO set greater than 7 = the BAM chain limit is 240KiB. SDB also takes into account the format of DSORG=PS or PS-E files, so you will get the appropriate blocking factor for the LRECL and format. The underlying data set will use a physical blocks size based on the max block specified for the data set, so unlike VSAM the physical block size is not remapped from the CISZ. I really don't see any upside to change this from half-track blocking. If you want to speed up BAM IO, then make sure you are using zHPF and set BUFNO=255. I don't think your application will notice the difference between 6.8MiB and 7.9MiB per SSCH, the TCW cost per SSCH for the controller is the same, and you may realize just how much you really wanted SSD or FMD drives. Ron -----Original Message----- From: IBM Mainframe Discussion List [mailto:IBM-MAIN@LISTSERV.UA.EDU] On Behalf Of Anne & Lynn Wheeler Sent: Friday, May 19, 2017 2:46 PM To: IBM-MAIN@LISTSERV.UA.EDU Subject: Re: [IBM-MAIN] SDB (system determined Blksize) <mailto:r.skoru...@bremultibank.com.pl> r.skoru...@bremultibank.com.pl (R.S.) writes: > Just curious: the formulas can give fractional values. How to round them? > OK, I assume the physrec/trk should be rounded down, but what about D? remember CKD disks haven't been manufactured for decades, all being simulated on industry standard FBA devices ... originally 512 byte fixed block ... but industry moving to 4k byte fixed block. In between are 4k FBA that simulate 512 byte. <https://en.wikipedia.org/wiki/Advanced_Format> https://en.wikipedia.org/wiki/Advanced_Format where you might have CKD simulated on 512 byte FBA simulated on 4096 byte FBA gets even more complex when RAID is layered over the top. -- virtualization experience starting Jan1968, online at home since Mar1970 ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to <mailto:lists...@listserv.ua.edu> lists...@listserv.ua.edu with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
