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Received: by minnie.vk1xwt.ampr.org with NNTP id AA1764 ; Tue, 23 Feb 93 14:56:59 EST Newsgroups: comp.unix.bsd Path: sserve!manuel.anu.edu.au!munnari.oz.au!news.Hawaii.Edu!ames!saimiri.primate.wisc.edu!zaphod.mps.ohio-state.edu!menudo.uh.edu!uuneo!sugar!karl From: karl@NeoSoft.com (Karl Lehenbauer) Subject: Re: [386BSD] What SCSI controllers _are_ supported? Organization: NeoSoft Communications Services -- (713) 684-5900 Date: Sat, 20 Feb 1993 00:34:41 GMT Message-ID: <C2q1Lu.7LJ@sugar.neosoft.com> Keywords: 386BSD SCSI References: <1993Feb17.214948.9390@fcom.cc.utah.edu> <C2no1H.1JDo@austin.ibm.com> <1993Feb19.033337.13588@fcom.cc.utah.edu> Lines: 20 In article <1993Feb19.033337.13588@fcom.cc.utah.edu> terry@cs.weber.edu (A Wizard of Earth C) writes: >My opinion unsubstantiated by testing: A cached controller is useless >for anything other than slowing initial transfer rates unless the controller >cache is *much* larger than the UNIX cache *and* the transfer rate between >the controller cache and memory is the same as that between memory and >memory. Spend your money on something you can see, like a big monitor. I agree with Terry (but also did not test). Also caching controllers change the order that writes are performed. It is important, at least for System V file systems, that blocks go out in the order the system wants them to go out in. The system thus ensures that the data of a file is out there before the inode is updated, and the inode is out there before the directory is updated, and so on, to insure that things aren't left weird and incomplete if the system crashes. Thus caching controllers that know nothing of the filesystem reduce the robustness of the filesystem. An UPS is mandatory, IMHO, if you are using a caching controller. -- -- Email info@NeoSoft.com for info on getting interactive Internet access. "I didn't have time to write a short letter, so I wrote a long one instead." -- Twain