Re: RAID6 12 device assemble force failure

[Adam Niescierowicz <adam.niescierowicz@justnet.pl>]

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On 3.07.2024 o 12:16, Mariusz Tkaczyk wrote:
> On Wed, 3 Jul 2024 09:42:53 +0200
> Mariusz Tkaczyk<mariusz.tkaczyk@linux.intel.com>  wrote:
>
> I was able to achieve similar state:
>
> mdadm -E /dev/nvme2n1
> /dev/nvme2n1:
>            Magic : a92b4efc
>          Version : 1.2
>      Feature Map : 0x0
>       Array UUID : 8fd2cf1a:65a58b8d:0c9a9e2e:4684fb88
>             Name : gklab-localhost:my_r6  (local to host gklab-localhost)
>    Creation Time : Wed Jul  3 09:43:32 2024
>       Raid Level : raid6
>     Raid Devices : 4
>
>   Avail Dev Size : 1953260976 sectors (931.39 GiB 1000.07 GB)
>       Array Size : 10485760 KiB (10.00 GiB 10.74 GB)
>    Used Dev Size : 10485760 sectors (5.00 GiB 5.37 GB)
>      Data Offset : 264192 sectors
>     Super Offset : 8 sectors
>     Unused Space : before=264112 sectors, after=1942775216 sectors
>            State : clean
>      Device UUID : b26bef3c:51813f3f:e0f1a194:c96c4367
>
>      Update Time : Wed Jul  3 11:49:34 2024
>    Bad Block Log : 512 entries available at offset 16 sectors
>         Checksum : a96eaa64 - correct
>           Events : 6
>
>           Layout : left-symmetric
>       Chunk Size : 512K
>
>     Device Role : Active device 2
>     Array State : ..A. ('A' == active, '.' == missing, 'R' == replacing)
>
>
> In my case, events value was different and /dev/nvme3n1 had different Array
> State:
>   Device Role : Active device 3
>     Array State : ..AA ('A' == active, '.' == missing, 'R' == replacing)

This kind of array behavior is like it should be?

Why I'm asking, in theory.

We have bitmap so when third drive disconnect from the array we should 
have time to stop the array in foulty state before bitmap space is over, 
yes?.
Next array send notification to FS(filesystem) that there is a problem 
and will discard all write operation.

Data that can't be store on the foulty device should be keep in the bitmap.
Next when we reatach missing third drive when we write missing data from 
bitmap to disk everything should be good, yes?

I'm thinking correctly?


> And I failed to start it, sorry. It is possible but it requires to work with
> sysfs and ioctls directly so much safer is to recreate an array with
> --assume-clean, especially that it is fresh array.

I recreated the array, LVM detected PV and works fine but XFS above the 
LVM is missing data from recreate array.

-- 
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Pozdrawiam
Adam Nieścierowicz

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