Re: Help needed - RAID5 recovery from Power-fail - SOLVED

["Nigel J. Terry" <nigel@nigelterry.net>]

Thanks for all the help. I am now up and running again and have been
stable for over a day. I will now install my new drive and add it to
give me an array of three drives.

I'll also learn more about Raid, mdadm and smartd so that I am better
prepared next time.

Thanks again

Nigel
Neil Brown wrote:
> On Monday April 3, nigel@nigelterry.net wrote:
>   
>> I wonder if you could help a Raid Newbie with a problem
>>
>> I had a power fail, and now I can't access my RAID array. It has been
>> working fine for months until I lost power... Being a fool, I don't have
>> a full backup, so I really need to get this data back.
>>
>> I run FC4 (64bit).
>> I have an array of two disks /dev/sda1 and /dev/sdb1 as a raid5 array
>> /dev/md0 on top of which I run lvm and mount the whole lot as /home. My
>> intention was always to add another disk to this array, and I purchased
>> one yesterday.
>>     
>
> 2 devices in a raid5??  Doesn't seem a lot of point it being raid5
> rather than raid1.
>
>   
>> When I boot, I get:
>>
>> md0 is not clean
>> Cannot start dirty degraded array
>> failed to run raid set md0
>>     
>
> This tells use that the array is degraded.  A dirty degraded array can
> have undetectable data corruption.  That is why it won't start it for
> you.
> However with only two devices, data corruption from this cause isn't
> actually possible. 
>
> The kernel parameter
>    md_mod.start_dirty_degraded=1
> will bypass this message and start the array anyway.
>
> Alternately:
>   mdadm -A --force /dev/md0 /dev/sd[ab]1
>
>   
>> # mdadm --examine /dev/sda1
>> /dev/sda1:
>>           Magic : a92b4efc
>>         Version : 00.90.02
>>            UUID : c57d50aa:1b3bcabd:ab04d342:6049b3f1
>>   Creation Time : Thu Dec 15 15:29:36 2005
>>      Raid Level : raid5
>>    Raid Devices : 2
>>   Total Devices : 2
>> Preferred Minor : 0
>>
>>     Update Time : Tue Mar 21 06:25:52 2006
>>           State : active
>>  Active Devices : 1
>>     
>
> So at 06:25:52, there was only one working devices, while...
>
>
>   
>> #mdadm --examine /dev/sdb1
>> /dev/sdb1:
>>           Magic : a92b4efc
>>         Version : 00.90.02
>>            UUID : c57d50aa:1b3bcabd:ab04d342:6049b3f1
>>   Creation Time : Thu Dec 15 15:29:36 2005
>>      Raid Level : raid5
>>    Raid Devices : 2
>>   Total Devices : 2
>> Preferred Minor : 0
>>
>>     Update Time : Tue Mar 21 06:23:57 2006
>>           State : active
>>  Active Devices : 2
>>     
>
> at 06:23:57 there were two.
>
> It looks like you lost a drive a while ago. Did you notice?
>
> Anyway, the 'mdadm' command I gave above should get the array working
> again for you.  Then you might want to
>    mdadm /dev/md0 -a /dev/sdb1
> is you trust /dev/sdb
>
> NeilBrown
>
>
>