Date: Thu, 21 Mar 1996 13:58:23 +1100 From: Bruce Evans <bde@zeta.org.au> To: andreas@knobel.gun.de, terry@lambert.org Cc: dave@kachina.jetcafe.org, freebsd-hackers@FreeBSD.org Subject: Re: Adding a damn 2nd disk Message-ID: <199603210258.NAA15921@godzilla.zeta.org.au>
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>> The command 'apropos disk' gives you lot's of ideas, where >> to search for pieces of information. The most important here: >> >> ... >> disklabel(5) - disk pack label >> disklabel(8) - read and write disk pack label >> disktab(5) - disk description file >> ... >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. >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designed to be on (no longer applicable) cylinder boundries, and 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 :-). Bruce
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