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Date:      Mon, 18 Jul 2011 16:49:25 +0200
From:      "DA Forsyth" <d.forsyth@ru.ac.za>
To:        freebsd-questions@freebsd.org
Subject:   how to fix bad superblock
Message-ID:  <4E2447F5.24958.3553D439@d.forsyth.ru.ac.za>

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Hiya all

After a hardrive let the smoke out last week, part of a 4 drive RAID 
array, I am now battling to get back into the array.
I have replaced the bad drive and it has been rebuilt (Intel Matrix 
Raid on the motherboard).

some partitions are ok but had lots of errors fsck fixed, others 
report 
** /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 UFS so why doesn't it look at block 
160?

'newfs -N ar0s1f' displays a lot of copies of the superblock.

Google show that this error happens to a lot of folks,a nd there is 
no tool for fixing it.  fsck_ufs will use an alternate superblock, 
prompt you to update the master block, and then NOT do it, the error 
persists.

I used a dd command I found on the web to copy an alternate SB to the 
master superblock, and fsck still shows the message as above.
I then copied the 2nd alternate to both the master and the 1nd 
alternate superblock positions, and it STILL reports a mismatch.

Please tell me, how do I fix this.  ar0s1f is discardable which is 
why I am trying to fix it first.  /home has stuff I want to recover 
and it also has a bad superblock.

The stuff I googled shows that there is confusion about block sizes.
When 'newfs -N' shows a copy at block 160, what block size does it 
mean?  the 16384 it shows in its display for this partition, or the 
default of 512?

Thanks

--
       DA Fo rsyth            Network Supervisor
Principal Technical Officer -- Institute for Water Research
http://www.ru.ac.za/institutes/iwr/





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