Date: Mon, 1 Apr 1996 13:04:37 -0700 (MST) From: Terry Lambert <terry@lambert.org> To: joerg_wunsch@uriah.heep.sax.de Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: fdisk and partition info Message-ID: <199604012004.NAA14051@phaeton.artisoft.com> In-Reply-To: <199603312229.AAA01348@uriah.heep.sax.de> from "J Wunsch" at Apr 1, 96 00:29:04 am
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> > > > What happens if you turn of translation on the things? > > > > I wonder how you wanna turn it off: [...] > > > Definitions for SCSI translation taking ZBR into account: > > > > Untranslated: H = Real number of heads > > C = Real number of cylinders > > S = ? (some average) > > C * H * S = Actual number of sectors, or less > > C/H/S is as reported by SCSI sense. > > However, these numbers are `real', but inaccessible. The SCSI > protocol doesn't let you enter any of these numbers in a SCSI command. > That's why you cannot turn off the ``translation''. Again, the translation I refer to is that which is done by the BIOS. Undetectable translation by hardware or controllers is never a problem. The WD1007 trnslation for sector sparing is a problem only because it is detectable (the controller-level geometry query includes the sparing sectors). ZBR translation is totally and completely transparent. It is only an issue if you want the disktab to be something other than a useless time-wasting frob, since the intent is to optimize disk activity to reduce the number of seeks (something which is impossible without knowledge of the real disk geometry, and on ZBR drives, is not possible without a vectored table lookup... and a SCSI II query). The SCSI I geometry query *will* return the real number of heads and cylinders. What it will not give is anything more than an average S value, rendering cylinder seek optimization useless. The term "untranslated" as used here refers to the geometry reported by INT 13 AH=8 in BIOS not differing from that reported by a controller query in protected mode. This is, in fact, impossible to achieve with Adaptec (and other) SCSI controllers, which do not support untranslated BIOS access (and a loss of cylinders over 1024). That the drive itself lies about the sector average to the SCSI I query (which would, ideally, be the same as what is reported by the BIOS query) is irrelevant. Terry Lambert terry@lambert.org --- Any opinions in this posting are my own and not those of my present or previous employers.
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