Debian 2.6.19 Mirror (RAID1) notes


After several years of using a RedHat 2.4 kernel, we upgraded to a Debian 2.6 Kernel by way of a Knoppix live CD.

These notes come from a RedHat RAID1command mindset and many years of using Linux (some steps may have been ommited, because Linux familiarity is assumed.)   If you are starting from scratch with mirroring concepts or Linux, do not waste your time here.  There is no need to learn Linux commands that are obsolete.  However, we cannot stop you from reading further : )

Most of the RAID commands (raidhotadd, mkraid, etc) fom RedHat do not exist on Debian, the /etc/raidtab no longer is used and is ignored if present.

The main command for RAID on Debian is mdadm

The Knoppix CD, and subsequent hard disk, loads everything it can find. We had spare mirror drives from the Redhat mirror to use for the Debian installation, and even though the file type for the partition was changed from Linux raid autodetect to Linux, the partitions were automatically started as part of a RAID configuration (/dev/md0, /dev/md1). The drive partition /dev/hdc2 was unable to be mounted. I believe the Superblock was detected, which is not visible to the user.

So, the first time using mdadm command was to stop the mirror: #mdadm –S /dev/md0

Prior to creation of the RAID1 array, the mirror drive needs to be partitioned and file systems created (mkswap, mkfs.ext3, mkfs.reiserfs, etc). You could wait to create the file system till after the RAID1 is created (mkfs.ext3 /dev/md1), if both drives are empty. The Knoppix CD created a Reiser File system as a default, which works great and is fast, but the creator of the file system (Hans Reiser) is in jail for killing his wife, which turned off many in using the system.

Creation of a mirror drive was not able to be accomplished for the active partition. Several attempts were made to write a superblock manually, but the partition was busy or the device /dev/md1 could not be found (Knoppix live CD). The primary mirror drive (the one with all the data) needs to be made a mirror by another drive running Debian and not a mirror drive – no superblock, as follows:

#mdadm –create –verbose /dev/md1 –level=1 –-raid-devices=2 missing /dev/hdd2 (/dev/hdd2 is the drive to be made a mirror drive, the boot drive was /dev/hda2 non-RAID)

After substituting the newly created mirror drive /dev/hdd2 as /dev/hda2, then rebooting (check entries in /etc/grub/menu.lst and /etc/fstab ex. Substitute /dev/hda2 with /dev/md1) [possibly need Linux rescue disk and vi editor], when the other mirror drive is available, the command would be:

#mdadm –a /dev/md1 /dev/hdd2 (essentially the raidhotadd command; drive /dev/hda2 is already part of the RAID array /dev/md1, created above --^)

A fast way to make a mirror drive from a blank disk:

Copy the MBR and partitions from the RAID1 drive   #dd if=/dev/hda of=/dev/hdc for 30 seconds, then ctrl+C.  Make the respective file systems  # mkwap /dev/hdc1  # mkfs.reiserfs /dev/hdc2   Reboot, then:  #mdadm –a /dev/md1 /dev/hdc2  #mdadm –a /dev/md0 /dev/hdc1

When trying to get mirroring working, /dev/md1 would not start because /dev/hda2 was pre-mounted (/etc/initramfs-tools/scripts/local-premount) for the boot from /boot/grub/menu.lst.  So, /dev/md1 needed to be specified in menu.lst instead of /dev/hda2.       In the process of trying various methods of making a superblock, the partition with the Reiser FS needed to be repaired:

#fsck.reiserfs –a –rebuild-sb /dev/md1

If one of the RAID1 partitions is swap space (/dev/md0), /etc/fstab should have the entry:

 /dev/md0 none swap sw 0 0

Initially there was a problem with the swap partition not being recognized. Another method to get the swap space mounted was to put a line in a startup script:

In /etc/rc.local :

/sbin/swapon /dev/md0

The command free displays the usage of  memory, in particular to note was the swap space being availabe.

#free
             total     used    free      shared     buffers     cached
Mem:        482760   428460   54300           0       50408      83096
-/+ buffers/cache:   294956  187804
Swap:      1024076       64 1024012

/etc/mdadm/mdadm.conf

DEVICE /dev/hda1 /dev/hdc1 /dev/hda2 /dev/hdc2
ARRAY /dev/md0 level=raid1 devices=/dev/hda1,/dev/hdc1
ARRAY /dev/md1 level=raid1 devices=/dev/hda2,/dev/hdc2

#mdadm --examine /dev/hda2

dev/hda2:
          Magic : a92b4efc
        Version : 00.90.00
           UUID : c397a21e:47354420:e759641f:3b75dba8
  Creation Time : Fri Dec 12 09:15:06 2008
     Raid Level : raid1
  Used Dev Size : 18526976 (17.67 GiB 18.97 GB)
     Array Size : 18526976 (17.67 GiB 18.97 GB)
   Raid Devices : 2
  Total Devices : 2
Preferred Minor : 1

    Update Time : Tue Dec 23 17:32:36 2008
          State : clean
 Active Devices : 2
Working Devices : 2
 Failed Devices : 0
  Spare Devices : 0
       Checksum : 6a760d21 - correct
         Events : 1482


      Number   Major   Minor   RaidDevice State
this     0       3        2        0      active sync   /dev/hda2

   0     0       3        2        0      active sync   /dev/hda2
   1     1      22        2        1      active sync   /dev/hdc2

#mdadm --examine /dev/hda1

 /dev/hda1:
          Magic : a92b4efc
        Version : 1.0
    Feature Map : 0x0
     Array UUID : 86347328:98224399:d51be4df:d918f459
           Name : 0
  Creation Time : Thu Dec 11 15:58:42 2008
     Raid Level : raid1
   Raid Devices : 2

 Avail Dev Size : 2048168 (1000.25 MiB 1048.66 MB)
     Array Size : 2048168 (1000.25 MiB 1048.66 MB)
   Super Offset : 2048176 sectors
          State : clean
    Device UUID : abbbb8f4:c08bdec4:cc4ed625:128f831f

    Update Time : Tue Dec 23 16:00:57 2008
       Checksum : 369d92dd - correct
         Events : 6


    Array Slot : 1 (failed, 1, 0)
   Array State : uU 1 failed

#mdadm --detail /dev/md0

 /dev/md0:
        Version : 01.00
  Creation Time : Thu Dec 11 15:58:42 2008
     Raid Level : raid1
     Array Size : 1024084 (1000.25 MiB 1048.66 MB)
  Used Dev Size : 1024084 (1000.25 MiB 1048.66 MB)
   Raid Devices : 2
  Total Devices : 2
Preferred Minor : 0
    Persistence : Superblock is persistent

    Update Time : Tue Dec 23 16:00:57 2008
          State : clean
 Active Devices : 2
Working Devices : 2
 Failed Devices : 0
  Spare Devices : 0

           Name : 0
           UUID : 86347328:98224399:d51be4df:d918f459
         Events : 6

    Number   Major   Minor   RaidDevice State
       2      22        1        0      active sync   /dev/hdc1
       1       3        1        1      active sync   /dev/hda1

#mdadm --detail /dev/md1

/dev/md1:
        Version : 00.90
  Creation Time : Fri Dec 12 09:15:06 2008
     Raid Level : raid1
     Array Size : 18526976 (17.67 GiB 18.97 GB)
  Used Dev Size : 18526976 (17.67 GiB 18.97 GB)
   Raid Devices : 2
  Total Devices : 2
Preferred Minor : 1
    Persistence : Superblock is persistent

    Update Time : Tue Dec 23 17:41:37 2008
          State : clean
 Active Devices : 2
Working Devices : 2
 Failed Devices : 0
  Spare Devices : 0

           UUID : c397a21e:47354420:e759641f:3b75dba8
         Events : 0.1482

    Number   Major   Minor   RaidDevice State
       0       3        2        0      active sync   /dev/hda2
       1      22        2        1      active sync   /dev/hdc2
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