And since a raid array usually hosts many volumes, utilization of the other volumes will impact a particular volume. And many site have multiple LPARs accessing some to all of the volumes on the array.
On Fri, Feb 7, 2014 at 9:27 AM, Joel C. Ewing <jcew...@acm.org> wrote: > On 02/06/2014 05:42 PM, Shmuel Metz (Seymour J.) wrote: >> In <bc6b7b77ef4d5e4bb95b0559a0d6d5e10531ce9...@mx3.state.nv.us>, on >> 02/06/2014 >> at 01:17 PM, "David G. Schlecht" <dschle...@admin.nv.gov> said: >> >>> Or am I way off base? >> >> At least partially. On a simulated 3390 a cylinder boundary may not >> tell you much about seek time, but it can still have an effect on >> whether a channel program breaks and has to be restarted. OTOH, with >> code that builds an ECKD channel program that has a lot less impact on >> performance than it used to. >> >> > ...and if the physical storage media still has an access-time function > which tends to be larger when separation on the physical media is > larger, it is not unreasonable to expect that any emulated 3390 strategy > which utilizes a fixed mapping would likely use some sequential > allocation strategy which would at least show a statistical bias for > faster access to blocks that were closer together on the emulated > device, as that would improve the odds (but not guarantee) they are > closer together on the physical media as well. Such access-time bias > would no doubt vary in a manner that couldn't be usefully predicted from > emulated DASD architecture, but it seems reasonable that it should > exist. In a practical sense though, one could argue that any data that > is being accessed frequently enough to be a performance concern would be > interacting with DASD cache storage in ways that could completely mask > the difference in physical access times; so the controlled placement of > VTOC, VTOCIX, and VVDS these days is more a matter of aesthetics and > emulated-media fragmentation avoidance than performance. > > -- > Joel C. Ewing, Bentonville, AR jcew...@acm.org > > ---------------------------------------------------------------------- > For IBM-MAIN subscribe / signoff / archive access instructions, > send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN -- Mike A Schwab, Springfield IL USA Where do Forest Rangers go to get away from it all? ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
