A 1.6.1 machine of mine has suddenly started crashing, for no apparent 
reason.  For the last crash, I deliberately left it not running X, so 
I could see any messages:

/tmp: got error 5 while accessing file system
panic: softdep_deallocate_dependencies: unrecovered I/O error

There were no messages indicating a hardware problem with the drive.

/tmp is mounted on /dev/sd1a.  The crash probably occurred when running 
/etc/daily; after some of the other crashes, I've seen indications of 
an I/O error on /tmp.

So -- is this a real I/O error?  I can read the partition using 'dd'.  
Should I reinitialize it with newfs?  Copy /dev/zero to it and then 
reinitialize?  Or is it a bug in softdep?  The problem occurred with a 
1.6.1 kernel from March, and also with one from a week ago, both times 
using the latest 1.6.x sources.

		--Steve Bellovin, http://www.research.att.com/~smb