Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!zaphod.mps.ohio-state.edu!uakari.primate.wisc.edu!dali.cs.montana.edu!milton!uw-beaver!Teknowledge.COM!unix!garth!fouts@bozeman.ingr.com (Martin Fouts) From: fouts@bozeman.ingr.com (Martin Fouts) Newsgroups: comp.sys.super Subject: Re: I/O subsystems (was Re: Supercomputer ROI) Message-ID: <424@garth.UUCP> Date: 6 Jun 90 19:37:23 GMT References: <201@csinc.UUCP> <253@garth.UUCP> <202@csinc.UUCP> <292@garth.UUCP> <10280@batcomputer.tn.cornell.edu> <359@garth.UUCP> <6374@amelia.nas.nasa.gov> Sender: fouts@garth.UUCP Distribution: na Organization: INTERGRAPH (APD) -- Palo Alto, CA Lines: 95 In-reply-to: yamo@wk46..nas.nasa.gov's message of 29 May 90 17:57:42 GMT In article <6374@amelia.nas.nasa.gov> (Michael Yamasaki) writes: In article <359@garth.UUCP> fouts@bozeman.ingr.com (Martin Fouts) writes: > >One of the ways in which cheap workstations got to be cheap was by >neglecting to install I/O hardware. [...] > >The single most frustrating thing for me as a consumer of workstations >is that I/O costs haven't decreased at the same relative rate as MIPS >and MFLOPS costs --- Although they are decreasing. [...] >However, the cost of I/O performance is coming down. ESDI drives with >hundreds of megabytes of storage are available on PCS which give the >same per user performance as the high performance I/O subsystems on >supercomputers at a lower per user cost, and usually much more storage >per user. > Greetings. IMHO, one of the places where supercomputers (my only experience is with Cray 2 and Cray YMP) excel over the touted killer micro solution is in I/O performance. In a strange way, it is because of the high cost of the traditional supercomputer that high cost/high performance I/O subsystems are acceptable. Your last statements are (in my experience) dubious. My workstation (a Personal Iris) gets something less than a megabyte/second disk I/O. Our Cray 2 gets something more than 10 megabytes/second. You know by the magic of large I/O buffers that it can seem to the user to get 30-40 megabytes/second. (Wasn't HSP-2's acceptance test something like an aggregate 100 MBytes/second?) Even with IPI-2 drives, workstations and PCs will quickly run out of I/O bus bandwidth. Add a HPPI or two, support for those million shaded polygons a second, a few hundred megabytes of memory, multiple micro processors and uh oh the main bus gets stressed a bit. There's more to supercomputer architecture than the CPU. When micros have sucessfully addressed the rest of the issues, then they'll really be "killers". Hi. I completely agree that the big systems are still much better at I/O. The requirement for HSP-2 by the way was for real aggragate disk performance across 10 pairs of drives at once, while maintaining an outrageous amount of network traffic. The Cray 2 passed with ease. (You can't actually generate enough I/O traffic across all of the disk drives, memory interfaces and high speed channels to consume the "backplane" rate that the machine can generate.) The much more recent Y/MP had to sweat a lot to pass, although it did eventually. Now let me try to justify my last point by pointing out that I said "per user". A typical PC has one user. A typical Cray 2 has thousands, often with dozens of users on running simultaneously. The raw performance of the workstation is often in the 1 to 10 percent range of the Cray, but the divisor is often 1 user for the workstation (how many people are you sharing the iris with?) and often 10 for simultaneous bandwidth and 1000 for storage for the Cray. By the way, through the magic of multiple busses, some Irises (I don't remember the personal well enough) can pass incredible amounts of data between the graphics engine and the display without ever touching the I/O bus. To reitterate, you are correct; the big win in supercomputer architecture is the scalability of I/O performance to match CPU performance. The big loose in "killer" microprocessor systems is the lack of that scalability. My argument is that we can build scalable workstations, if we are willing to concentrate on the i/o as well as the CPU. One of the things which frustrates me in this area is the lack of educational effort. The latest book on computer "architecture" from two people who should know better spends most of its time on CPU performance and devotes only a small portion to I/O architecture. Of course, it is much better than typical "architecture" texts which only deal with CPU architecture. -Yamo- yamo@wk46.nas.nasa.gov yamo@amelia.nas.nasa.gov {ncar, decwrl, hplabs, uunet}!ames!amelia!yamo (hey, Marty, you gonna show up for some softball one of these days? -Y-) (When's the next game. Scuba class is over, but nobody has sent me a schedule in thee weeks.) -- Martin Fouts UUCP: ...!pyramid!garth!fouts ARPA: apd!fouts@ingr.com PHONE: (415) 852-2310 FAX: (415) 856-9224 MAIL: 2400 Geng Road, Palo Alto, CA, 94303 If you can find an opinion in my posting, please let me know. I don't have opinions, only misconceptions.