Re: MD RAID6 corrupted by Avago 9260-4i controller [SOLVED]

Wolfgang Denk
2016-05-16T10:06:42Z

Dear Andreas,

In message <20160516083903.GA29380@EIS.leimen.priv> you wrote:
>
> You are using your disks in alphabetical order, are you sure this is
> the same order your RAID originally used? Maybe the drive letters
> changed?

Yes, this is one thing I am absolutely sure about. I have the mapping
of the disk serial numbers from initial install, and I verified that
the drive order is still the same.

> You found LABELONE on sda, which is your first drive (Device Role 0)
> in your RAID (see mdadm --examine after you create it), but when I
> create a new RAID based on loop devices, pvcreate and vgcreate it,
> the LABELONE actually appears on the 2nd drive (Device Role 1).

Thi sis strage; I see you are using 6 disks and the same stripe size,
so I would also expect a layout like yours. OK, I need to experiment
a bit...

> So I assume in the default left-symmetric layout in RAID6, the first chunk
> of the first disk actually ends up being a parity chunk...? I'm not too
> sure about this either right now. ;)

Hm... is --data-offset the only parameter I can play with? (except for
variations of drive order, which appear to make no sense to me as I'm
sure I have it correct).

Then I could also start a brute force approach and just try out all
possible values until I gind a match ;-)

Best regards,

Wolfgang Denk

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