Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!clyde.concordia.ca!uunet!mcsun!ukc!dcl-cs!aber-cs!rupert!pcg From: pcg@rupert.cs.aber.ac.uk (Piercarlo Grandi) Newsgroups: comp.sys.hp Subject: Re: Disk performance HP-UX 6.5 Message-ID: Date: 18 Dec 89 18:59:58 GMT References: <2437@ifi.uio.no> <17330009@hpfcdj.HP.COM> Sender: pcg@aber-cs.UUCP Organization: Coleg Prifysgol Cymru Lines: 45 In-reply-to: kinsell@hpfcdj.HP.COM's message of 16 Dec 89 01:15:29 GMT [somebody has done this test:] > dd if=/dev/ of=/dev/null bs=8k count=2000 >and the time (measured with /bin/time) it takes do this is >Sun 3/80 with SunOS 4.03 real: 18.4 sys: 8.2 >HP 9000/370 with HP-UX 6.5 real: 144.8 sys: 9.1. In article <17330009@hpfcdj.HP.COM> kinsell@hpfcdj.HP.COM (Dave Kinsell) writes: Using dd with the block special device file isn't doing what you think it's doing. [ ...some comments about read ahead buffering... ] Actaully, what's happening here isn't what you think either. Read ahead buffering in the device does not enter the picture at all. SunOS 4 does ALL io (save raw devices!) via memory mapping of files (including block devices as well I believe), and does not read data in, if that's written to /dev/null immediately thereafter (this because of copy-on-write). Try doing 'time cp /vmunix /dev/null' under SunOS 4, SunOS 3, and HP-UX, and you will see; especially if run under the C shell, that gives you a count of IO operations. Otherwise we would be seeing a miracolous 1 MByte a sec out of SunOS, and I do not believe in miracles; in much the same conditions, but with SunOS 3.5 on a 3/50, I get real: 151 and sys: 17, which are compatible with the slower CPU speed of the 3/50 w.r.t. the 3/80; I do not think that SunOS 4 has drivers and a filesystem that are 10 times as fast as SunOS 3, because they are largely the same. In other words, the numbers posted above by somebody are completely bogus, and it is my general impression that HP-UX and SunOS are really within the same league of IO bandwidth. The only machines that seem to have decent or above average IO bandwidth are the MIPSco ones, and they took a lot of care in that. -- Piercarlo "Peter" Grandi | ARPA: pcg%cs.aber.ac.uk@nsfnet-relay.ac.uk Dept of CS, UCW Aberystwyth | UUCP: ...!mcvax!ukc!aber-cs!pcg Penglais, Aberystwyth SY23 3BZ, UK | INET: pcg@cs.aber.ac.uk