From owner-freebsd-geom@FreeBSD.ORG  Wed Nov 17 03:44:45 2004
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From: Suleiman Souhlal <ssouhlal@FreeBSD.org>
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Date: Tue, 16 Nov 2004 22:44:36 -0500
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Subject: Severe gbde problem
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Hello,

I was able to verify that there is a pretty severe problem with gbde, as
noted in http://www.freebsd.org/cgi/query-pr.cgi?pr=72812 :

I enabled gbde_swap in a 5.3 installation running inside qemu, and after
running a few processes making large mallocs, the following message
appeared on the console:

swap_pager: I/O error - pageout failed; blkno 5610,size 4096,error 0

After rebooting, the system was unbootable (stuck at boot0). Apparently,
it has overwritten parts of the disklabel, or something similar.

The swap partition was right at the beginning of the disk. In a previous
(failed) attempt to reproduce this problem, the swap partition was
actually the second partition on the disk, and none of the symptoms
happened.

So, it seems that gbde is overwriting bytes that are just before its
partition.

Any ideas on how to track this bug down?

Bye,
-- 
Suleiman Souhlal    | ssouhlal@vt.edu
The FreeBSD Project | ssouhlal@FreeBSD.org