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Path: sserve!newshost.anu.edu.au!munnari.oz.au!bunyip.cc.uq.oz.au!harbinger.cc.monash.edu.au!yarrina.connect.com.au!warrane.connect.com.au!kralizec.zeta.org.au!not-for-mail From: bde@kralizec.zeta.org.au (Bruce Evans) Newsgroups: comp.os.386bsd.bugs Subject: Re: 1.1 won't boot on my 486 && slow access of pcfs volumes Date: 8 Jul 1994 19:52:47 +1000 Organization: Kralizec Dialup Unix Sydney - +61-2-837-1183, v.32bis v.42bis Lines: 26 Message-ID: <2vj7lf$24c@kralizec.zeta.org.au> References: <CsKz06.BD0@helios.physics.utoronto.ca> NNTP-Posting-Host: kralizec.zeta.org.au In article <CsKz06.BD0@helios.physics.utoronto.ca>, Jacques Legare <jacques@helios.physics.utoronto.ca> wrote: >2) Anyone notice that accesses to a pcfs floppy are deathly slow. This is because the buffer cache barely works for pcfs floppies. The block size for pcfs floppies is only 512 bytes, so it takes 2880 buffers to cache a single 1440K floppy. FreeBSD allocates only about 345 buffers on a 16M system (and less than 1/4 of that on a 4M system) so the cache often thrashes. (FreeBSD assigns only a small number of buffers to avoid certain memory fragmentation and overallocation problems. It calculates the number based on an average block size of 4K, so when the average block size is 8 times smaller, 7/8 of the cache is wasted.) The cache usually works better for pcfs on hard disks because the block size is larger. > Even worse a command like 'cp /mnt/drive-a/* /tmp' seems to be > uninteruptible and worse seems to prevent access to the target drive. It probably doesn't really hang. Probably all the buffers are getting assigned to reading the floppy so accesses to the hard disk have to wait for the floppy. -- Bruce Evans bde@kralizec.zeta.org.au