Date: Tue, 19 Jul 2011 14:28:57 +0200 From: "DA Forsyth" <d.forsyth@ru.ac.za> To: freebsd-fs@freebsd.org Cc: freebsd-questions@freebsd.org Subject: How to fix bad superblock on UFS2? Message-ID: <4E257889.12343.39F99213@d.forsyth.ru.ac.za>
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Hi all
I had a drive let out smoke, it was part of a 4 drive RAID5 array on
an intel Matrix motherboard controller (device ar). Having fought
various battles just to get the machine to boot again (had to upgrade
to 7.4 from 7.2 to do it because of a panic in ataraid.c) I now have
some partitions reporting superblock problems. Havign googled
around this topic for some hours now, and having tried copying one or
more of the backup superblocks to the primary and secondary (at block
160), I still get....
** /dev/ar0s1f
BAD SUPER BLOCK: VALUES IN SUPER BLOCK DISAGREE WITH THOSE IN FIRST
ALTERNATE
it then asks if it must look for alternates but claims 32 is not one
and stops. All my partitions are UFS2 so why doesn't it look at
block 160, which 'newfs -N' finds correctly as the next superblock
copy?
So, how do I fix this?
Also, why does fsck_ufs prompt to update the primary superblock when
you give it an alternate with '-b xx', and then not do it?
I have now tried booting from the FreeBSD 8.2 live CD in the hopes
that the most recent fsck will actually fix this, but it does not.
One thing I found in my web searching is that there is confusion over
block sizes. 'newfs -N' appears to report sector counts as block
addresses.
Doing
dd if=/dev/ar0s1fbs=512 skip=160 count=16 | hd -v | grep "54 19"
bears this out as the output does indeed contain the correct magic
number. 'fsck_ufs -b 160 /dev...' also works as expected, but then
you try 'fsck /dev/...' and it will report the bad superblock, and
then fail to find any backup superblocks, which newfs managed just
fine, and this might be because the disk thinks blocks are 16384 in
size.
Thanks
--
DA Fo rsyth Network Supervisor
Principal Technical Officer -- Institute for Water Research
http://www.ru.ac.za/institutes/iwr/
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