Date: Thu, 21 Mar 1996 02:51:32 -0700 (MST) From: Terry Lambert <terry@lambert.org> To: bde@zeta.org.au (Bruce Evans) Cc: andreas@knobel.gun.de, terry@lambert.org, dave@kachina.jetcafe.org, freebsd-hackers@FreeBSD.org Subject: Re: Adding a damn 2nd disk Message-ID: <199603210951.CAA29401@phaeton.artisoft.com> In-Reply-To: <199603210258.NAA15921@godzilla.zeta.org.au> from "Bruce Evans" at Mar 21, 96 01:58:23 pm
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> >Stop right there. > > >the concept of "disktab" is fundamentally flawed. It assumes that > >it is not possible to determine the disk size from the controller, > >and it assumes uniform boundry recording for seek optimization. > > Well, it isn't always possible. It fails for old MFM drives and for > floppies (floppies may be unformatted, or formatted with a nonstandard > number of sectors/track ...). /etc/disktab is still useful for holding > the defaults for such mouldy drives. Yick. Formatting should take care of this... the floppy driver should auto-detect format. The format has to be specified and done seperately anyway. The driver for old MFM drives should read the CMOS drive table. > >The seek optimization is, in reality, useless because ZBR media > >makes it very difficult (without SCSI II extended queries) to > >determine the real cylinder boundries to do the optimization. > > The old drives don't use ZBR. The optimization is broken in another way > for floppies - since the number of sectors/cylinder is only one or wwo > times larger than the smallest possible (ufs) block size and not a > multiple of the block size, many blocks span cylinder boundaries. > > >This baically leaves default sector sparing settings, sector counts > >designed to be on (no longer applicable) cylinder boundries, and > >slice geometries that should be interactively determined instead > >of frozen in an obsolete data file. > > >The disktab should go. > > I see that you have sold your stock of ESDI drives :-). No, but I see that the slice code forces a translated world view (fake cylinder boundries) on me pretty much anyway, unless I go to an extrordinary amount of effort. Now that you mention it, I would like to see code written for ZBR drives, at least the ones that could be queried with SCSI II. 8-). 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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