Good information all, I was basing it off the JCL manual.
I rarely get a chance to dig through the DS Macros, or DFHSMS Manuals, or some of the other more technical manuals, which is why I never caught that change. However it still is a good idea to try to match buffering to today's LBI devices. (64K for Cart, 128K for Tape Silo's, and I -think- DASD after 3390-09's transfers at 256K LBI) It gives the speed advantage of LBI usage without having to try and use the LBI interface directly from programs. (I'll admit I never tried using LBI directly at all, as adequate buffering based on the LBI (Transfer) size seems to accomplish the same thing) Not arguing that it would make sense if SMS or the OS could be enhanced to default buffering for a file based on the LBI of its device. Which begs another question; is there any storage devices left on mainframes that are not LBI? Darren -----Original Message----- From: IBM Mainframe Discussion List [mailto:[EMAIL PROTECTED] On Behalf Of Ed Gould Sent: Wednesday, October 31, 2007 11:00 AM To: [email protected] Subject: Re: z/OS 1.9 Features summary On Oct 31, 2007, at 10:24 AM, GAVIN Darren * OPS EAS wrote: > I beg to differ right back, the default buffering is 2, according > to the > IBM Manuals. Your shop might have changed that through SMS. Some > places > do that. > > <Snip>In truth, the physical geometry is largely > Unknown and most of the data is actually returned from some level of > cache, > where blocksizes mean nothing (since gaps don't exist).</Snip> > > And I will differ with you on this point as well, as I've done my own > testing of Buffering sizes based on Data Transfer Sizes (that are > readily available in the manuals) and that matching them is the most > efficient way to do I/O. Once the Data leaves the cache of the > devices, > it is transferred at a certain size/rate. Matching that size with > additional buffers means that less actual I/O requests are made to the > channel. > > Darren > IBM made the default for QSAM data sets (20 or so years ago) to 5 and the default is for chained scheduling (for QSAM ) at the same time. This was accomplished by integrating SAMe into DFSMS. 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
