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From: Chris Torek <torek@torek.net>
To: Da Rock <freebsd-fs@herveybayaustralia.com.au>, freebsd-fs@freebsd.org
Subject: Re: Delete a directory, crash the system
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Date: Wed, 01 Apr 2015 01:12:59 -0700
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> ... run fsck after a crash ... will allow you to recover from
> media errors which it appears your system is suffering from.
> SU+J is just a faster way of restarting but only works when you
> do not have media errors.

It's worth adding that this is also needed after some non-media
memory errors (on systems lacking ECC, which -- alas -- includes
my main home system) that corrupt bits in FFS bitmaps and
directories, which are then written back to the (perfectly good)
medium.

(I had a bad DRAM chip that memtest86+ found for me, that until I
replaced it caused broken file systems, that after I replaced it
in turn caused panics followed by inappropriate journal recovery.
There's really nothing to do here other than force the fsck.)

Chris