From owner-freebsd-hackers Fri May 31 09:28:12 1996 Return-Path: owner-hackers Received: (from root@localhost) by freefall.freebsd.org (8.7.5/8.7.3) id JAA22077 for hackers-outgoing; Fri, 31 May 1996 09:28:12 -0700 (PDT) Received: from mole.mole.org (marmot.mole.org [204.216.57.191]) by freefall.freebsd.org (8.7.5/8.7.3) with SMTP id JAA22069 for ; Fri, 31 May 1996 09:28:06 -0700 (PDT) Received: (from mail@localhost) by mole.mole.org (8.6.12/8.6.12) id QAA03760; Fri, 31 May 1996 16:28:03 GMT Received: from meerkat.mole.org(206.197.192.110) by mole.mole.org via smap (V1.3) id sma003758; Fri May 31 16:27:51 1996 Received: (from mrm@localhost) by meerkat.mole.org (8.6.12/8.6.9) id JAA21316; Fri, 31 May 1996 09:27:51 -0700 Date: Fri, 31 May 1996 09:27:51 -0700 From: "M.R.Murphy" Message-Id: <199605311627.JAA21316@meerkat.mole.org> To: bde@zeta.org.au, freebsd-hackers@freefall.freebsd.org, sextonr.crestvie@squared.com Subject: Re: Disktab and SCSI Performance. Sender: owner-hackers@FreeBSD.ORG X-Loop: FreeBSD.org Precedence: bulk > > -d 0 > Rotdelay is only useful for slow disks. All small nonzero rotdelays are > equivalent to skipping every second block, i.e., to using an interleave > of 2 for blocks. This is in addition to any hardware interleave, and has > much the same disaadvantages as hardware interleave: an interleave of N > reduces the best-case performance by a factor of N. Disks with their > Iown read _and_ write buffering don't need to be interleaved at the block > level. For disks with read but not write buffering, you can use -d 0 > to get the best possible read performance but abysmal write performance, > or -d 4 to get medicocre performance for both read and write. > Rotdelay and/or artificially increased interleave can be useful for fast disks, too. It can be used to prevent a fast drive on a non-dma controller from starving the CPU to the exclusion of user programs. Sometimes slowing disk I/O can be an advantage. From experience :-) -- Mike Murphy mrm@Mole.ORG +1 619 598 5874 Better is the enemy of Good