Date: Fri, 31 May 1996 09:27:51 -0700 From: "M.R.Murphy" <mrm@MARMOT.Mole.ORG> To: bde@zeta.org.au, freebsd-hackers@freefall.freebsd.org, sextonr.crestvie@squared.com Subject: Re: Disktab and SCSI Performance. Message-ID: <199605311627.JAA21316@meerkat.mole.org>
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> > -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
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