Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucsd!sdcc6!sdcc13!pa1159 From: pa1159@sdcc13.ucsd.EDU (pa1159) Newsgroups: comp.arch Subject: Re: *big iron* Message-ID: <1186@sdcc13.ucsd.EDU> Date: 29 Sep 89 00:54:17 GMT References: <21962@cup.portal.com> <1989Sep12.031453.22947@wolves.uucp> <22130@cup.portal.com> <1989Sep16.044013.429@wolves.uucp> <259@ssp1.idca.tds.philips.nl> <22308@cup.portal.com> <7981@cbmvax.UUCP> <11538@burdvax.PRC.Unisys.COM> <22488@cup.portal.com> <24950@lou Reply-To: pa1159@sdcc13.ucsd.edu.UUCP (pa1159) Organization: Univ. of California, San Diego Lines: 47 In article <24950@louie.udel.EDU> nelson@udel.EDU () writes: >In article <22488@cup.portal.com> cliffhanger@cup.portal.com (Cliff C Heyer) writes: >> >Since we are talking about "*big iron*", let's talk about real big iron. >Cray DD-40 disk drives can support >10MB/sec through the operating >system (at least COS; I assume the case is also true for UNICOS). >And COS also supports disk striping at the user level, so for >sequential reads of a file striped across an entire DS-40 disk >subsystem (20+ GB, 4 drives) a process can achieve sustained rates >of 40MB/sec. Of course, this is for relatively large (~ 0.5MB) >reads, but these aren't uncommon for the sort of processing Crays >do. > This brings up a point: in what processing regimes does total sustained disk tranfer rate be the performance-limiting factor? For a mini/single-user workstation configuration I'd think that the average access time rather than sustained throughput would be most important as most I/O transfers would be relatively small. So, given equal access times, how much of a difference in interactive workloads does a jump from say 500 KB/s (low end micro disks) to 3-4 MB/s make in performance? Of course, for things like massive image processing applications sustained throughput is a Good Thing, but for the Rest Of Us, how much does it really matter? Matt Kennel pa1159@sdcc13.ucsd.edu PS: The Connection Machine parallel disk subsystem is pretty nifty. 40 simultaneous bitstreams, which when error-corrected &c make a 32-bit word per tick. You can trash one drive and then reconstruct its contents from the 39 others. I don't know the numbers, but I suspect that it's very fast. l>Disk I/O is one of Cray's big selling points vs. the Japanese >super-computer manufacturers--their machines generally have >mainframe (read 4MB/sec) style disk channels. > >Mark Nelson ...!rutgers!udel!nelson or nelson@udel.edu >This function is occasionally useful as an argument to other functions >that require functions as arguments. -- Guy Steele