Keep forgetting that changed. So to amend what I said, the best minimum in my example would be BUFNO=8 (2 128k Large Blocks or 1 256k large block)
Darren -----Original Message----- From: IBM Mainframe Discussion List [mailto:[EMAIL PROTECTED] On Behalf Of Ed Gould Sent: Wednesday, February 13, 2008 3:44 PM To: [email protected] Subject: Re: 3590 stacking performance via JCL? On Feb 13, 2008, at 3:44 PM, GAVIN Darren * OPS EAS wrote: > Most of the Performance on tape drives can be accomplished by matching > the BUFNO= parameter to the Devices I/O Data Transfer Size. For your > model that's probably (most Tapes and VTS are) a 128kb size, so you > would want enough buffering to hold at least 1 128k Large Block. > > So for a BLKSIZE=32768 file you would want a BUFNO=4 at minimum, but > would be better off with BUFNO=16 or BUFNO=32 (4 or 8 Large Blocks) as > Some VTS Units and the 256 track 3590E have a 256kb Transfer Size. > > However DFSORT ignores any buffering (It has its own I/O context) on > both DASD and TAPE so no need to use it when doing sorts. > > The other thing you can do is to add a step at start of job that will > Pre-Mount the tapes and then Retain them for any following steps, > using > IEFBR14 as a stub program, and the VOL=(,RETAIN) option mentioned > earlier. > > There is also the /*setup card that can be used on some JES systems. > > Darren > > Darren, I am fairly sure that the default for QSAM is 5 buffers if you decrease it to 4 you will have a negative impact on performance. Ed ---------------------------------------------------------------------- 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
