In article <21281@life.ai.mit.edu> I wrote:
>My understanding has always been that
>if you had a swap partition at the beginning of a disk, you would
>eventually get your disk label (and partition info) swapped on, and die
>horribly, so I've always avoided this configuration.
It turns out that since SunOS 4.0 (at least), swapping has been handled
carefully by the kernel: the first block of every partition is
skipped, so it's no longer possible to clobber the label. (However,
if you use cylinder zero as a raw device, e.g. for a database, it *is*
still possible to wipe out the label.)
The following piece of kernel comment from swap_init() bears this out:
/*
* To prevent swap I/O requests from crossing the boundary
* between swap areas, we erect a "fence" between areas by
* not allowing the first page of each swap area to be used.
* (This also prevents us from scribbling on the disk label
* if the swap partition is the first partition on the disk.)
* This may not be strictly necessary, since swap_blksize also
* prevents requests from crossing the boundary.
*/
Thanks to the following for sending me facts (and opinions):
Tad Guy <tadguy@ab00.larc.nasa.gov>
dupuy@hudson.cs.columbia.edu (Alexander Dupuy)
Thomas Weihrich <Thomas.Weihrich@arbi.informatik.uni-oldenburg.de>
essick@i88.isc.com (Raymond Essick)
chinson@cs.ucla.edu (Chinson Yi)
Mike.Sullivan@ebay.sun.com (Mike Sullivan { Nowhere Man })
-- Chris Metcalf, MIT Laboratory for Computer Science metcalf@catfish.lcs.mit.edu // (617) 253-7766
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