Re: sdc1 does not have a valid v0.90 superblock, not importing!

--- On Wed, 11/8/10, Neil Brown <neilb@suse.de> wrote:

From: Neil Brown <redacted>
Subject: Re:  sdc1 does not have a valid v0.90 superblock, not importing!
To: Jon@eHardcastle.com
Cc: jd_hardcastle@yahoo.com, linux-raid@vger.kernel.org
Date: Wednesday, 11 August, 2010, 12:06
On Wed, 11 Aug 2010 02:55:44 -0700
(PDT)
Jon Hardcastle [off-list ref]
wrote:

quoted

(my first attempt appears to have been bounced as the

spam checker thought it had HTML in it?!)

odd... came through ok for me the first time.

quoted

Help!

Long story short - I was watching a movie off my RAID6

array. Got a smart error warning

quoted

Aug 10 22:00:07 mangalore kernel: raid5: cannot start

dirty degraded array for md4

This is the current problem.  The array is dirty and
degraded so there could
theoretically be undetectable corruption.  Chance is
quite low but it is
there so md won't start with out you acknowledging the risk
by giving the
--force flag to mdadm --assemble.
Only do that if you are confident that your hardware is
working correctly.

Well I am reasonable sure the controller came adrift the first time.. when i reseated it i stopped getting 100's of errors.. and it has survived 1.5 badblocks checks. It is being held in place by one of those bars you press down (does all the expansion cards in 1 go) except i dont think it is very good. I will screw it down.

quoted

It appears sdc has an invalid superblock?

This is the 'examine' from sdc1 (note the checksum)

/dev/sdc1:

.....

quoted

      Checksum : b335b4e3 -

expected b735b4e3

Single bit error.  That isn't good as it means some
bit of memory or some bit
on some bus somewhere cannot be trusted.
It could be a transient thing and will never happen
again.  Or maybe not.
Given the smart errors and the fact that you have had
problems with the drive
before it seem very likely that the problem is in that
drive.  I suggest
unplugging it and leaving it unplugged.  Some memory
buffer in the drive is
probably marginal.  I don't think they use ECC
memory.

Could this be a result of me forcing a power off when the drive was causing problems?

What are the dangers to removing it, zeroing the superblock and readding? is it MORE dangerous than leaving a raid 6 degraded for a few days?

quoted

Anyways... I am ASSUMING mdadm has not assembled the

array to be on the safe side? i have not done anything.. no
force... no assume clean.. I wanted to be sure?

You assume correctly.

quoted

Should i remove sdc1 from the array? It should then

assemble? I have 2 spare drives that I am getting around to
using to replace this drive and the other 500GB.. so should
I remove sdc1... and try and re-add or just put the new
drive in?

quoted

atm I have 'stop'ped the array and got badblocks

running....

quoted

Remove sdc and assemble the array with --force, and get a
new device to
replace /dev/sdc as soon as possible.

Thanks Neil - I panic'd as previously it has mounted the array in a degraded state... but previously the drive has disappeared completely... whereas in this case it is present... but wrong!

NeilBrown
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