--- 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, 12:34
On Wed, 11 Aug 2010 04:19:07 -0700
(PDT)
Jon Hardcastle [off-list ref]
wrote:

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

wrote:

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From: Neil Brown <redacted>
Subject: Re:  sdc1 does not have a valid

v0.90 superblock, not importing!

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To: Jon@eHardcastle.com
Cc: jd_hardcastle@yahoo.com,

linux-raid@vger.kernel.org

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Date: Wednesday, 11 August, 2010, 12:06
On Wed, 11 Aug 2010 02:55:44 -0700
(PDT)
Jon Hardcastle [off-list ref]
wrote:

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(my first attempt appears to have been

bounced as the

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spam checker thought it had HTML in it?!)

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

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Help!

Long story short - I was watching a movie

off my RAID6

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array. Got a smart error warning

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Aug 10 22:00:07 mangalore kernel: raid5:

cannot start

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dirty degraded array for md4

This is the current problem.  The array is dirty

and

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degraded so there could
theoretically be undetectable corruption. 

Chance is

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quite low but it is
there so md won't start with out you

acknowledging the risk

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by giving the
--force flag to mdadm --assemble.
Only do that if you are confident that your

hardware is

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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.

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It appears sdc has an invalid superblock?

This is the 'examine' from sdc1 (note the

checksum)

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/dev/sdc1:

.....

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      Checksum : b335b4e3 -

expected b735b4e3

Single bit error.  That isn't good as it means

some

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bit of memory or some bit
on some bus somewhere cannot be trusted.
It could be a transient thing and will never

happen

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again.  Or maybe not.
Given the smart errors and the fact that you have

had

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problems with the drive
before it seem very likely that the problem is in

that

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drive.  I suggest
unplugging it and leaving it unplugged.  Some

memory

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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?

Probably not.  Forcing a power off may well have left
the array 'dirty' so
that it wouldn't assemble, but is fairly unlikely to
corrupt data within a
block.

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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?

In general, I would say the chance of a known-bad drive
causing problems is
greater than the chance of a fewer known-good drives
causing problems.
But then you seem to think it isn't the drive, it was the
controller and that
is fixed...

This is really about your level of trust in the hardware.
If you trust sdc as much as the others, include it in the
array.
If you don't, then don't.

NeilBrown

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Anyways... I am ASSUMING mdadm has not

assembled the

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array to be on the safe side? i have not done

anything.. no

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force... no assume clean.. I wanted to be sure?

You assume correctly.

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Should i remove sdc1 from the array? It

should then

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assemble? I have 2 spare drives that I am getting

around to

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using to replace this drive and the other 500GB..

so should

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I remove sdc1... and try and re-add or just put

the new

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drive in?

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atm I have 'stop'ped the array and got

badblocks

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running....

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Remove sdc and assemble the array with --force,

and get a

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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!

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NeilBrown
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For the benefit of those that follow! I assemble the array by specifying exactly the drives I wanted in it.. once assembled i could confidently zero-block the troublesome drive... without it rearing its ugly head again!

I now have a 1 drive down - degraded raid 6 array.


      
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