How to fsck a mounted raid device /dev/md2 ?

Shamsul Kamal
Shamsul Kamal used Ask the Experts™
on
Hi,

I would like to request an assistant.

It seems that my /var/log/messages having the following error message :

Jan  1 11:24:26 srv9 kernel: raid1: sdb: unrecoverable I/O read error for block 286895360

My cat /proc/mdstat shows as follows :

root@srv9 [~]# cat /proc/mdstat
Personalities : [raid1]
md0 : active raid1 sdb1[1] sda1[0]
      104320 blocks [2/2] [UU]

md1 : active raid1 sdb2[1] sda2[0]
      2096384 blocks [2/2] [UU]

md2 : active raid1 sda3[2](S) sdb3[1]
      310367680 blocks [2/1] [_U]


My mdadm --detail /dev/md2 shows as follows :

root@srv9 [/]# mdadm --detail /dev/md2
/dev/md2:
        Version : 0.90
  Creation Time : Fri May 30 17:11:49 2008
     Raid Level : raid1
     Array Size : 310367680 (295.99 GiB 317.82 GB)
  Used Dev Size : 310367680 (295.99 GiB 317.82 GB)
   Raid Devices : 2
  Total Devices : 2
Preferred Minor : 2
    Persistence : Superblock is persistent

    Update Time : Tue Jan  1 23:24:58 2013
          State : clean, degraded
 Active Devices : 1
Working Devices : 2
 Failed Devices : 0
  Spare Devices : 1

           UUID : 273f6c1b:0e438923:11f1305b:25e0df37
         Events : 0.9388326

    Number   Major   Minor   RaidDevice State
       0       0        0        0      removed
       1       8       19        1      active sync   /dev/sdb3

       2       8        3        -      spare   /dev/sda3



SUMMARY
=========


1. /var/log/messages shows sdb which having the error.
2. /proc/mdstat shows sda3[2](S) device which is degraded and becoming spare.
3. /dev/sdb3 is my actual /dev/md2 current active mounted partition .

I believe my /dev/sdb3 is having filesystem error that need to be fixed but it is actually current active raid partition.

May i know the simplest way to fsck the drive ? If possible without boot it using linux rescue disk ?

I found the following article :

http://wiki.sabayon.org/index.php?title=HOWTO:_Repair_filesystem_using_fsck_on_a_raid_setup

But in the article does not mentioned that i need to unmounted the /dev/md2 device first , afaik the fsck must be run on unmounted device to avoid data corruption.

FYI, the /dev/sdb3 is still active mounted as /dev/md2 .

Should i fsck /dev/sda3 or /dev/sdb3 ? and how ?


Appreciates anybody assistant on this.

Thank you.
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DavidPresident
Top Expert 2010

Commented:
You DON'T fsck a mounted device, at least not if you want to prevent data corruption.
  Boot the system to a USB stick with linux on it, then fsck.
Shamsul KamalJunior Tech

Author

Commented:
Hi,

Do you mean the following articles is wrong ?

http://wiki.sabayon.org/index.php?title=HOWTO:_Repair_filesystem_using_fsck_on_a_raid_setup

It does not unmounted the /dev/md2 before fsck right ?
President
Top Expert 2010
Commented:
Yes it is wrong.   Read this, it is derived from the kernel.org and the authors of the mdraid code itself ..

http://www.tldp.org/HOWTO/Software-RAID-0.4x-HOWTO-4.html
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Commented:
not recommended at all to run fsck with mounted partition.
Julian ParkerSenior Systems Administrator

Commented:
What is it mounted as?

If it's prt of the operating system then you'll need to boot from other medi, if not then try unmounting it
Shamsul KamalJunior Tech

Author

Commented:
Hi,

It is mounted as "/" .

So i guest eventhough it is a raid array, i still need to boot using other media and fsck it.
DavidPresident
Top Expert 2010

Commented:
yes.

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