Re: RAID6 recovery with 6/9 drives out-of-sync

[Phil Turmel <philip@turmel.org>]

On 06/01/2016 07:32 AM, Peckins, Steven E wrote:
> 
> On May 31, 2016, at 2:19 PM, Phil Turmel <philip@turmel.org> wrote:
> 
>> On 05/30/2016 10:43 PM, Peckins, Steven E wrote:
>>>
>>> The component devices in the array are supposed to be multipath devices (dm-multipath), but for some reason, when the server was restarted, md grabbed both dm-* components and raw devices.  I *think* that this is what caused the problem.
>>
>> Quite possible.  You probably need a DEVICES clause in your mdadm.conf
>> to exclude the raw devices from the arrays.
> 
> I had a typo in the DEVICE glob for the system disks (/dev/sd[ab]* instead of /dev/sd[ab][12]).

Understood, but be aware that if you have to hotswap one of these system
devices, they may not get the sda or sdb name, preventing a re-add or a
replacement from joining the array.

Since you are having to use /dev/mapper entries for some arrays,
consider using /dev/disk/by*/ symlinks for your system arrays.

>>> I'm seeking advice on how to proceed at this point.  If more information is required, please ask.
>>
>> Hmmm.  The partial success on mdadm --force suggests trying that again.
>> Possible with --force twice on the command line.
>>
>> Forced assembly is precisely what you need -- don't despair and attempt
>> anything else.
> 
> Repeating the command was not successful; it is still reporting "/dev/md10 assembled from 5 drives and 1 spare - not enough to start the array."  Four drives are listed as “possibly out of date."  I assume those are the four that are not being incorporated.
> 
> Output from --assemble --force 1x and 2x:  http://pastebin.com/k1dT2zYC

{ In the future, please paste these in-line so the archives will have
them.  The size limit for this list is ~ 100k. }

I vaguely recall a bug in forced reassembly for many out-of-date drives.
 Please clone and build the latest mdadm userspace[1] and run that mdadm
binary for the forced assembly.  Also show the portion of dmesg that
corresponds to the attempt.

Phil

[1] https://github.com/neilbrown/mdadm

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