Date: Fri, 17 Mar 1995 19:12:32 +1000 From: Bruce Evans <bde@zeta.org.au> To: terry@cs.weber.edu, wollman@halloran-eldar.lcs.mit.edu Cc: current@FreeBSD.org, phk@ref.tfs.com, rgrimes@gndrsh.aac.dev.com Subject: Re: newfs: sectors per cylinder (4096) disagrees with disk label (36) Message-ID: <199503170912.TAA12937@godzilla.zeta.org.au>
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>Let me point out that: >> # of SCSI disks > == >> > # of SCSI controllers >> > * # of SCSI devices per bus >> > * # of SCSI LUNs The bits for this aren't allocated yet. There are 16 to spare. >AND >> * # of slices (regular and extended) + 1 > == >> > * # of partitions (regular and extended) > + 1 (to grant you an unnecessary abstraction that can be > worked around by adding a single ioctl) + 2 actually. 5 bits are allocated. >AND >> * # of BSD partitions per slice > == >> > * # of BSD slices per partition > + an irrelevent terminology change 3 bits are allocated. >Before you go off on "# of SCSI controllers" vs. "major numbers", >note that I did include this option in the unquoted portion of >my post. It only reduces the need to less than 32 bits but still >more than the 16 bits you'd expect. There are 8 major bits and 24 minor bits. See the major() and minor() macros in <sys/types.h>. >The number of devices that must be addressed is the relevent issue, >not how one chooses to address them (although adding (n+1)/n times >the number of devices does strike me as particularly inelegant). 2^24 is plenty of devices! Naming them right is harder. I once had MAKEDEV generating about 700 disk devices but have reduced that to about 200 (27 per unit) by only generating partitions for the first BSD partition. This required naming the first BSD partition canonically. I don't really like this - it's like renumbering SCSI devices. Bruce
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