Bill, With XA I don't think that RPS was ever included in connect time. I admit I only started working on XA in 1984, but everything I had from back then by Beretvas and Freisenborg uses disconnect time to estimate if there is a seek problem based on RPS being counted in Disconnect time.
Of course this was focused on 3880 Controllers. I have no idea if it was different for earlier models that required reconnect for handling TIC. Ron > -----Original Message----- > From: IBM Mainframe Discussion List [mailto:ibm-m...@bama.ua.edu] On Behalf Of > Bill Fairchild > Sent: Friday, August 14, 2009 6:24 AM > To: IBM-MAIN@bama.ua.edu > Subject: Re: [IBM-MAIN] Degraded I/O performance in 1.10? > > You're right. It spun at 70 revolutions per second. The 3380 spun at 60 rps, > so its revolution took 16.67 ms. > > The average latency of a disk drive was useful for calculating connect time > when every I/O probably involved a real seek (disconnect time) and a real > partial revolution for the search loop to find the correct record (which was > all connect time). But with today's hardware, caching, RAID, channel speed, > controller buffering, etc., the connect time component should consist almost > totally of data transfer. 1/2 revolution's worth of data transfer indicates > the average amount of data to be transferred per I/O is 1/2 of a full track. > Since EXCP tells SMF to add one to its I/O counters not for every I/O request > but rather for every block being transferred, then RMF's reported connect time > for these I/Os should vary widely if BUFNO is varied widely, say from one to > ten, while the EXCP counted reported by SMF would be constant. > > I don't doubt the validity of the IBM number at the time it was published > (aeons ago). I doubt its validity for today's hardware. I am only trying to > guess why IBM recommended that number aeons ago in the face of its obvious > inapplicability today. > > Bill Fairchild > > Software Developer > Rocket Software > 275 Grove Street * Newton, MA 02466-2272 * USA > Tel: +1.617.614.4503 * Mobile: +1.508.341.1715 > Email: bi...@mainstar.com > Web: www.rocketsoftware.com > ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@bama.ua.edu with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
