Re: RAID-5 and mdadm --assemble troubleshooting

[NeilBrown <neilb@suse.de>]

On Mon, 21 Mar 2011 23:08:40 +0100 A J Wyborny <ajwyborny@gmail.com> wrote:

> Hi all,
> 
> After exhausting my efforts with google searches and linux-raid IRC
> chats, I'm reaching out to you all for some help with why I can't
> assemble a broken RAID-5 configuration.  My initial problem, I've
> determined, was caused by a faulty PCI-E SATA controller card.  I
> would constantly lose access to my mounted RAID volume (/home) at
> random times and increasingly during high write accesses.  In the past
> a reboot and running "mdadm --assemble --force --scan" would solve the
> issue.  This time, no such luck.  In the process of troubleshooting I
> also fat-fingered an "mdadm --assemble" command and lost the
> superblock of my /dev/sda1 partition, which isn't helping things
> either.
> 
> The SMART status is clean on all disks.
> 
> I really appreciate any thoughts/input you might have.  -Adam
> 
> Here's my setup:
> 
> RAID-5 array with four 1.5TB disks (/dev/sda1, /dev/sdb1, /dev/sdd1, /dev/sde1)
> /dev/sdc is my root and swap partitions
> /dev/md0 should be mounted to /home
> 
> Results:
> root@focalor:~# cat /proc/mdstat
> Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5]
> [raid4] [raid10]
> unused devices: <none>
> root@focalor:~# mdadm -vv --assemble --force --scan
> mdadm: looking for devices for /dev/md0
> mdadm: cannot open device /dev/sdc1: Device or resource busy
> mdadm: /dev/sdc1 has wrong uuid.
> mdadm: no RAID superblock on /dev/sda1
> mdadm: /dev/sda1 has wrong uuid.
> mdadm: /dev/sde1 is identified as a member of /dev/md0, slot 3.
> mdadm: /dev/sdd1 is identified as a member of /dev/md0, slot 2.
> mdadm: /dev/sdb1 is identified as a member of /dev/md0, slot 1.
> mdadm: no uptodate device for slot 0 of /dev/md0
> mdadm: added /dev/sdd1 to /dev/md0 as 2
> mdadm: added /dev/sde1 to /dev/md0 as 3
> mdadm: added /dev/sdb1 to /dev/md0 as 1
> mdadm: failed to RUN_ARRAY /dev/md0: Input/output error

You are hitting an mdadm bug fixed in 2.6.9 by 

http://neil.brown.name/git?p=mdadm;a=commitdiff;h=4e9a6ff778cdc58dcc6897e74cf5ee1d3f73e1f7

What version of mdadm are you running?

You can work around it by
  echo 1 > /sys/module/md_mod/parameters/start_dirty_degraded

before running the 'mdadm -A' command.


> dmesg output:
> http://pastebin.com/usrzvmpn
> 
> mdadm -E output:
> http://pastebin.com/vnaamC75

It is OK - even encouraged - to include this content directly in the Email.
That makes it easier to reference in a reply, should that be helpful.

NeilBrown

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