Date: Wed, 3 Apr 1996 12:40:22 +0930 (CST) From: Michael Smith <msmith@atrad.adelaide.edu.au> To: bde@zeta.org.au (Bruce Evans) Cc: luigi@labinfo.iet.unipi.it, msmith@atrad.adelaide.edu.au, davidg@Root.COM, dutchman@spase.nl, freebsd-hackers@freebsd.org Subject: Re: HDD cpu usage (IDE vs. SCSI). Message-ID: <199604030310.MAA17901@genesis.atrad.adelaide.edu.au> In-Reply-To: <199604021147.VAA11954@godzilla.zeta.org.au> from "Bruce Evans" at Apr 2, 96 09:47:18 pm
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Bruce Evans stands accused of saying: > > >No, you're not understanding. For a given CPU, IDE will _always_ use more > >CPU time than SCSI. Period. > > Really? Please give numbers for a PIO mode 4 IDE controller vs an ST01 > SCSI controller :-). Please give numbers for your choice of controllers > vs my choices of applications an i/o access patterns. I'll choose a > memory intensive application that stalls the CPU waiting for the SCSI > controller. I'll arrange the i/o so that memory caching is defeated > at strategic places. Grrr, pedant 8) I'll show you a pile of happy users who've said "wow, that's so much faster", and "gee, I was going to replace the CPU" when finally talked into using SCSI for their production systems. > >If you have lots of free CPU, then IDE is fine, but if you feel that your > >CPU has better things to do with its time than copy data to and from > >your disk, then SCSI is the only solution that makes sense. > > I think lots of free CPU is the usual case. E.g., right now on freebsd.org: > > 3:40AM up 19 days, 11 mins, 16 users, load averages: 0.41, 0.32, 0.31 These are averages, and have little or no bearing on the 'feel' of a system, particularly during 'peaky' loads (starting an X application is a good example 8). > I would prefer lower latency to lower overhead in most cases. IDE disks > have natural advantages in this area (no complicated SCSI protocol to > interpreted by the slow i/o processor on the controller). Presuming you only have one application making requests in a linear fashion, that's fine. Tagged queueing and disconnect rapidly improves things once you start to get busy though. You're arguing out of character, which is confusing. Stop it 8) > Bruce -- ]] Mike Smith, Software Engineer msmith@atrad.adelaide.edu.au [[ ]] Genesis Software genesis@atrad.adelaide.edu.au [[ ]] High-speed data acquisition and (GSM mobile) 0411-222-496 [[ ]] realtime instrument control (ph/fax) +61-8-267-3039 [[ ]] Collector of old Unix hardware. "Where are your PEZ?" The Tick [[
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