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#1 2012-03-05 09:29:15

Registered: 2012-03-04
Posts: 7

[SOLVED] RAID 1 reverts to "read only" after reboot

After 2 years of using Archlinux on laptops (although still a newbie) I thought I would try it on my main machine. Never asked a question on these forums as usually all answers here, but now I am stuck.

Setup is fakeraid using mdadm. From /dev/as[ab] made a RAID0 (/dev/md125) which works and boots up Archlinux and Windows. RAID1 (/dev/md126) is for my data storage.

cat /proc/mdstat

md125 : active raid0 sda[1] sdb[0]
      904921088 blocks super external:/md127/0 128k chunks
md126 : active (read-only) raid1 sda[1] sdb[0]
      524297216 blocks super external:/md127/1 [2/2] [UU]
md127 : inactive sda[1](S) sdb[0](S)
      5024 blocks super external:imsm
unused devices: <none>

Cannot do anything to mount partition on md126 to write (can be mounted for read only).
mdadm --readwrite /dev/md126 reports no errors, but md126 remain read only

However, after:
mdadm --stop /dev/md126
sudo mdadm --assemble --scan

It works, and mountable for write!

After reassemble:
cat /proc/mdstat

md125 : active raid0 sda[1] sdb[0]
      904921088 blocks super external:/md127/0 128k chunks

Relevant /etc/mkinitcpio.conf

MODULES="dm_mod raid0 raid1 ext4 piix"
HOOKS="base udev autodetect pata scsi sata filesystems usbinput mdadm_udev"

mdstat --detail /dev/md126

      Container : /dev/md/imsm0, member 1
     Raid Level : raid1
     Array Size : 524297216 (500.01 GiB 536.88 GB)
  Used Dev Size : 524297348 (500.01 GiB 536.88 GB)
   Raid Devices : 2
  Total Devices : 2

          State : clean 
 Active Devices : 2
Working Devices : 2
 Failed Devices : 0
  Spare Devices : 0

           UUID : 19ffe6ac:b17ac771:c8f6de71:7e7f0eb6
    Number   Major   Minor   RaidDevice State
       1       8        0        0      active sync   /dev/sda
       0       8       16        1      active sync   /dev/sdb

cat /etc/mdadm.conf

ARRAY /dev/md/imsm0 metadata=imsm UUID=519871c0:298af950:19d92799:ba926f0d
ARRAY /dev/md/Volume0 container=/dev/md/imsm0 member=0 UUID=b59ca13e:b4c47dc8:0eac16bc:ee37fea4
ARRAY /dev/md/Volume1 container=/dev/md/imsm0 member=1 UUID=19ffe6ac:b17ac771:c8f6de71:7e7f0eb6

Now if I reboot, md126 becomes read-only again.
I wonder if I need something else in mkinitcpio.conf. Any advice of where else I should look would be helpful.

Last edited by poppyfields (2012-03-05 10:34:23)


#2 2012-03-05 10:06:56

Registered: 2008-02-10
Posts: 223

Re: [SOLVED] RAID 1 reverts to "read only" after reboot

Yes, yes, imsm raids tend to do that. Before the mdadm_udev hook mdassemble segfaulted so I couldn't even use MDraid and had to use DM-raid.
Running `mdmon md127` should cause it to become auto-read-only, and the next read-write mount makes it writable.
It seems that adding /sbin/mdmon to BINARIES in mkinitcpio.conf fixes this, since it will also be executed. So give that a try smile

However, you have to make sure that before the last poweroff/reboot command in the shutdown process, the raid mounts are all at least remounted as read-only, otherwise it tends to always want to resync the raid on boot...
Or at least it does here...

(imsm-)raids are annoying.

Last edited by Blµb (2012-03-05 10:08:09)

You know you're paranoid when you start thinking random letters while typing a password.
A good post about vim
Python has no multithreading.


#3 2012-03-05 10:33:09

Registered: 2012-03-04
Posts: 7

Re: [SOLVED] RAID 1 reverts to "read only" after reboot

Thanks for the advice - it worked. I had a lot of segfaulted errors and therefore used mdadm_udev. Been thinking of getting a dedicated hardware RAID card to avoid all this in future. It took over a week to sort the RAID issues out for me. At least it woks (for now wink ). Have to say - great support on this forum!


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