Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!pacific.mps.ohio-state.edu!zaphod.mps.ohio-state.edu!swrinde!ucsd!ucsdhub!hp-sdd!ncr-sd!ncrlnk!ncrwic!encad!entec!jlohmeye From: jlohmeye@entec.Wichita.NCR.COM (John Lohmeyer) Newsgroups: comp.periphs.scsi Subject: Re: SCSI hiding geometry Summary: SCSI allows you control everything...or not! Message-ID: <526@entec.Wichita.NCR.COM> Date: 15 Mar 90 00:42:28 GMT References: <1660@aber-cs.UUCP> <51507@sgi.sgi.com> <132788@sun.Eng.Sun.COM> <1990Mar11.045128.17732@ico.isc.com> <1990Mar11.220934.23771@light.uucp> Reply-To: jlohmeye@entec.Wichita.NCR.COM (John Lohmeyer) Organization: NCR Corporation, Wichita, KS Lines: 43 Keywords: In article <1990Mar11.220934.23771@light.uucp> bvs@light.UUCP (Bakul Shah) writes: >In article <1990Mar11.045128.17732@ico.isc.com> rcd@ico.isc.com (Dick Dunn) >writes: >> [deleted] >>Frankly, I don't want to trust J Random Microcoder to give a disk-write- >>reordering algorithm that won't screw things up. Even if I'm assured of >>some sort of "fair" algorithm, trying to sequence things in the kernel to >>compensate for all the possible variants of reordering sounds like a pain. >>(It's also redundant in a perverse way: You have to write code to un-do >>decisions which are going to be made for you that you don't want.) > >I will second that. > >Some more points: > [Interesting points about why the os can do it better omitted in follow-up] You guys really ought to read the SCSI-2 draft standard before complaining about "smart" disks and controllers. There are methods to control or not control these features to your heart's content. If you want to control queue re-ordering, use an ORDERED queue tag. If you want to see the drive geometry, there are gobs of controls in the mode pages. You can even deal with notched drives (a.k.a., zone bit recording), but it is ugly. Most people would rather let the drive deal with the variable number of blocks per cylinder than try to manage it. There are controls to enable/disable automatic sparing. There is a READ LONG command that you can use to try to recover trashed blocks. You can even control whether or not error recovery is employed. In short, if you really want to manage these things, you can do so. If you would rather spend your time on other things and let the drive manage itself, you can do that. Please send me email if there are any controls we left out -- there is always SCSI-3. :-) -- John Lohmeyer J.Lohmeyer@Wichita.NCR.COM NCR Corp. uunet!ncrlnk!ncrwic!entec!jlohmeye 3718 N. Rock Rd. Voice: 316-636-8703 Wichita, KS 67226 SCSI BBS 316-636-8700 300/1200/2400 24 hours