Re: Problem recovering a failed RIAD5 array with 4-drives.

[James <LinuxKernel@jamesplace.net>]

> On Thu, Jul 12, 2007 at 08:49:15AM -0500, James wrote:
> > My apologies if this is not the correct forum. If there is a better place 
to 
> > post this please advise.
> > 
> > 
> > Linux localhost.localdomain 2.6.17-1.2187_FC5 #1 Mon Sep 11 01:17:06 EDT 
2006 
> > i686 i686 i386 GNU/Linux
> > 
> > (I was planning to upgrade to FC7 this weekend, but that is currently on 
hold 
> > because-)
> > 
> > I've got a problem with a software RIAD5 using mdadm.
> > Drive sdc failed causing sda to appear failed. Both drives where marked 
> > as 'spare'.
> > 
> > What follows is a record of the steps I've taken and the results. I'm 
looking 
> > for some direction/advice to get the data back. 
> > 
> > 
> > I've tried a few cautions things to bring the array back up with the three 
> > good drives with no luck. 
> > 
> > The last thing attempted had some limited success. I was able to get all 
> > drives powered up. I checked the Event count on the three good drives and 
> > they were all equal. So I assumed it would be safe to do the following. I 
> > hope I was not wrong. I issued the following commands to try to bring the 
> > array into a usable state.
> > 
> > 
> > 
> > 
> > []# 
> > 
mdadm --create --verbose /dev/md0 --assume-clean --level=raid5 --raid-devices=4 --spare-devices=0  /dev/sda1 /dev/sdb1 /dev/sdc1 /dev/sdd1
> 
> Don't you want assemble rather than create if it already exists?
> 
> How did two drives fail at the same time?  Are you running PATA drives
> with two drives on a single cable?  That is a no no for raid.  PATA
> drive failures often take out the bus and you never want two drives in a
> single raid to share an IDE bus.
> 
> You probably want to try and assemble the non failed drives, and then
> add in the new replacement drive afterwards, since after all it is NOT
> clean.  Hopefully the raid will accept back sda even though it appeared
> failed.  Then you can add the new sdc to resync the raid.
> 
> --
> Len Sorensen
> 

I should have included more information. When I attempted to --assemble the 
array I received the following:

[]# mdadm --assemble [--force --run] /dev/md0 /dev/sda1 /dev/sdb1 
[/dev/sdc1]  /dev/sdd1
mdadm: failed to RUN_ARRAY /dev/md0: Input/output error


>From what I read I assumed I could use the --assume-clean option with --create 
to bring the array back at least in some semblance of working order. 

I'd like to recover as much as possible from the RAID array. I actually have a 
nice new SATA configuration sitting here waiting to receive the data. This 
thing failed a day too early. I'm gnashing my teeth over this one. 

I'd truly appreciate any help/advice.