Moving your Linux root partition to software RAID

Update 2012-01-18: This guide has been updated for recent changes, and is safe to use on current Ubuntu and Debian releases.

One of the reasons I started this blog is to write about problems I’ve solved that I can’t find answers to already on the web. Today, let’s talk about moving your linux install to linux software raid (md raid / mdadm). This post assumes you are running Ubuntu Linux 8.04, but any Debian-based distro from the past two years, or most other distros, will have similar commands.

We start with an install on a single 80 GB SATA drive, partitioned as follows:

/dev/sda1 as /, 10GB, ext3, bootable
/dev/sda2 as swap, 1GB
/dev/sda3 as /home, 69GB, ext3

We want to add a second 80GB SATA drive and move the entire install to use RAID1 between the two drives. So the final configuration will appear:

/dev/md0 as /, 10GB, ext3
/dev/md1 as swap, 1GB
/dev/md2 as /home, 69GB, ext3

Where the raid arrays are:

md0 : active raid1 sda1[0] sdb1[1]
md1 : active raid1 sda2[0] sdb2[1]
md2 : active raid1 sda3[0] sdb3[1]

Here there be dragons. As always, back up your data first. If you don’t know how to use rsync, now is an excellent time to learn.

The general plan is:

  1. Partition the new drive
  2. Create RAID arrays and filesystems on the new drive
  3. Copy the data from drive 1 to the new RAID arrays on drive 2
  4. Install grub on drive 2
  5. Configure fstab and mdadm.conf, and rebuild initramfs images
  6. Reboot on the RAID arrays on drive 2
  7. Repartition drive 1 and add it to RAID

All commands are run as root. Use sudo if you prefer.

Step 1: Partition the new drive

Assuming you want to partition the second drive the same way as the first, this is easy. Just clone the partitions from /dev/sda to /dev/sdb:

sfdisk -d /dev/sda | sfdisk /dev/sdb

You may want to format the new disk first to clear it of old data, especially if it previously had software RAID partitions on it. You may get unusual results if it has a similar partition structure or RAID setup as the original disk.

Now use parted to mark the partitions for software RAID, with the first partition to boot:

parted /dev/sdb
(parted) toggle 1 raid
(parted) toggle 2 raid
(parted) toggle 3 raid
(parted) toggle 1 boot
(parted) print

Disk /dev/sdb: 80.0GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos

Number  Start   End     Size    Type     File system  Flags
 1      0.51kB  10.0GB  10.0GB  primary  ext3         boot, raid
 2      10.0GB  11.0GB  2000MB  primary  linux-swap   raid
 3      11.0GB  80.0GB  69.0GB  primary  ext3         raid
(parted) quit

Parted will show you a file system in each partition, but the reality is that they will be plain linux software raid partitions (type 0xfd):

fdisk -l /dev/sdb

Disk /dev/sdb: 80.0 GB, 80026361856 bytes
255 heads, 63 sectors/track, 9729 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0xa3181e57

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1   *           1        1216     9765625   fd  Linux RAID autodetect
/dev/sdb2            1216        1338      976562+  fd  Linux RAID autodetect
/dev/sdb3            1338        9730    67408556   fd  Linux RAID autodetect

Step 2: Create RAID arrays and filesystems on the new drive

Now we create RAID 1 arrays on each partition. These arrays will have just one member each when we create them, which isn’t normal for RAID 1. So we’ll have to force mdadm to let us:

apt-get install mdadm
mdadm --create /dev/md0 --level=1 --force --raid-devices=1 /dev/sdb1
mdadm --create /dev/md1 --level=1 --force --raid-devices=1 /dev/sdb2
mdadm --create /dev/md2 --level=1 --force --raid-devices=1 /dev/sdb3

Next, you’ll need to create filesystems on the new RAID devices. Assuming the same formats as your first partition:

mkfs.ext3 /dev/md0
mkswap /dev/md1
mkfs.ext3 /dev/md2

Step 3: Copy the data from drive 1 to the new raid arrays on drive 2

This is a job for rsync. First, there are some directories on a running Linux system that we do not want to copy, like /dev and /proc. We also want to ignore tempfs directories, like /var/run. The best way to avoid these is to make an excludes file. Create a file, /root/rsync-filter, with the following content.

If running Ubuntu 11.10 or newer:

- /dev/
- /home/*/.gfvs
- /lib/modules/*/volatile/
- /mnt/
- /proc/
- /run/
- /sys/

If running earlier releases:

- /dev/
- /home/*/.gfvs
- /lib/modules/*/volatile/
- /mnt/
- /proc/
- /sys/
- /var/lock/
- /var/run/

These lines define directories we will not copy over. You may wish to add /tmp, apt’s cache, etc, but if you do you must manually create the directories themselves on the new filesystem.

Mount the new RAID array:

mount /dev/md0 /mnt
mkdir /mnt/home
mount /dev/md2 /mnt/home

If you are using a different mount structure, just be sure to recreate it and mount it in the right places in the new filesystem under /mnt/.

And start the rsync copy:

rsync -avx --delete -n --exclude-from /root/rsync-filter / /mnt/
rsync -avx --delete -n /home/ /mnt/home/

You will see a list of files that will be changed, but nothing actually happens. This is the job of the -n argument, which performs a dry-run. Always do this before actually starting a copy. You WILL make a painful mistake with rsync some day, so learn to be cautious. Repeat the above commands without the -n when you are sure all is well.

The -x argument ensures that you will not cross filesystem boundaries, which is why you must copy /home separately, and any other mounted filesystems. If you omit this you only need one command. But make sure you have a good rsync filter file, and that you have nothing mounted like /media/cdrom that you don’t want an archive of.

Finally, create the directories that you skipped with your filter. If running Ubuntu 11.10 or newer:

cd /mnt/
mkdir -p dev/ mnt/ proc/ run/ sys/
for i in /lib/modules/*/volatile ; do mkdir -p /mnt/$i ; done

If running earlier releases:

cd /mnt/
mkdir -p dev/ mnt/ proc/ sys/ var/lock/ var/run/
for i in /lib/modules/*/volatile ; do mkdir -p /mnt/$i ; done

Step 4: Install grub on drive 2

OK, we almost have a working RAID install on the second drive. But it won’t boot yet. Let’s use chroot to switch into it.

mount --rbind /dev /mnt/dev
mount --rbind /proc /mnt/proc
chroot /mnt

Now we have a working /dev and /proc inside the new RAID array, and by using chroot we are effectively in the root of the new array. Be absolutely sure you are in the chroot, and not the real root of drive 1. Here’s an easy trick: make sure nothing is in /sys:

ls /sys

If not, you’re in the new chroot.

Now we need to update grub to point to the UUID of the new filesystem on the RAID array. Get the UUID of /dev/md0’s filesystem:

tune2fs -l /dev/md0 | grep UUID

Filesystem UUID:          8f4fe480-c7ab-404e-ade8-2012333855a6

We need to tell grub to use this new UUID. How to do this depends on which version of grub you are using.

Step 4.1: If you are using GRUB 2, which is the default on Ubuntu since 9.10 Karmic Koala:

Edit /boot/grub/grub.cfg and replace all references to the old UUID with the new. Find all the lines like this:

search --no-floppy --fs-uuid --set 9e299378-de65-459e-b8b5-036637b7ba93

And replace them with the new UUID for /dev/md0:

search --no-floppy --fs-uuid --set 8f4fe480-c7ab-404e-ade8-2012333855a6

Do not run grub-mkconfig, as this will undo your changes. Install grub on the second drive.

grub-install /dev/sdb

Go on to step 5 below.

Step 4.2: If you are using GRUB 1 (Legacy), which is the default on Ubuntu before 9.10 Karmic Koala:

Edit grub’s and menu.list files. Edit /boot/grub/ and make sure both drives are listed:

(hd0)   /dev/sda
(hd1)   /dev/sdb

Edit /boot/grub/menu.list and find the line like this:

# kopt=root=UUID=9e299378-de65-459e-b8b5-036637b7ba93 ro

Replace the UUID with the one you just found. Leave the line commented, and save the file. Now rebuild menu.lst to use the new UUID:


Double-check that each boot option at the bottom of menu.lst is using the right UUID. If not, edit them too. Finally, install grub on the second drive.

grub-install /dev/sdb

Step 5: Configure fstab and mdadm.conf, and rebuild initramfs images

We’re almost ready to reboot. But first, we need to build an initramfs that is capable of booting from a RAID array. Otherwise your boot process will hang at mounting the root partition. Still in the chroot, edit /etc/fstab and change the partition entries to the new filesystems or devices.

If your /etc/fstab has “UUID=” entries like the following, change them to the new entries:

proc            /proc           proc    defaults        0       0
UUID=8f4fe480-c7ab-404e-ade8-2012333855a6 /               ext3    relatime,errors=remount-ro 0       1
UUID=c1255394-4c42-430a-b9cc-aaddfb024445 none            swap    sw              0       0
UUID=94f0d5db-c525-4f52-bdce-1f93652bc0b1 /var/           ext3    relatime 0       1
/dev/scd0       /media/cdrom0   udf,iso9660 user,noauto,exec,utf8 0       0

In the above example, the first UUID cooresponds to /dev/md0, the second to /dev/md1, and so on. Find the UUIDs with:

/lib/udev/vol_id /dev/md0

If your distribution uses a newer udev, you may not have the vol_id command. Use:

/sbin/blkid /dev/md0

If your /etc/fstab has “/dev/sda1” entries like it’s a bit easier. Just change them to /dev/md0 and so on:

proc            /proc           proc    defaults        0       0
/dev/md0        /               ext3    relatime,errors=remount-ro 0     1
/dev/md1        none            swap    sw              0       0
/dev/md2        /var/           ext3    relatime        0       1
/dev/scd0       /media/cdrom0   udf,iso9660 user,noauto,exec,utf8 0       0

Now, while still in the chroot, edit /etc/mdadm/mdadm.conf to list each RAID array:

DEVICE partitions
ARRAY /dev/md0 UUID=126a552f:57b18c5b:65241b86:4f9faf62
ARRAY /dev/md1 UUID=ca493308:7b075f97:08347266:5b696c99
ARRAY /dev/md2 UUID=a983a59d:181b32c1:bcbb2b25:39e64cfd

Find the UUID of each RAID array, which is not the same as the UUID of the filesystem on it (!), using mdadm:

mdadm --detail /dev/md0 | grep UUID

Now, rebuild your current kernel’s initramfs image:

update-initramfs -u

Or all of them:

update-initramfs -u -k all

Step 6: Reboot on the RAID arrays on drive 2

Now we’re ready to reboot. First, exit the chroot and power off the machine cleanly. You have three options:

  1. If your BIOS allows you to select which drive to boot from, elect to boot from drive 2.
  2. Swap drives 1 and 2 so drive 2 becomes /dev/sda, and restart
  3. Use a USB recovery stick to boot from drive 2

When the system restarts, you should reboot on the new RAID drive. Make sure:

df -h

Filesystem            Size  Used Avail Use% Mounted on
/dev/md0              9.2G  1.9G  6.9G  21% /
varrun                498M   56K  498M   1% /var/run
varlock               498M     0  498M   0% /var/lock
udev                  498M   68K  498M   1% /dev
devshm                498M     0  498M   0% /dev/shm
lrm                   498M   39M  459M   8% /lib/modules/2.6.24-19-generic/volatile
/dev/md2               63G  130M   60G   1% /home

Step 7: Repartition drive 1 and add it to RAID

Finally, we add the old drive into the array. Assuming you chose option 1 and didn’t swap the drive’s cables:

sfdisk -d /dev/sdb | sfdisk --force /dev/sda

If you receive a warning message here, reboot now.

Re-reading the partition table ...
BLKRRPART: Device or resource busy
The command to re-read the partition table failed
Reboot your system now, before using mkfs

If not, continue on:

mdadm /dev/md0 --grow -n 2
mdadm /dev/md1 --grow -n 2
mdadm /dev/md2 --grow -n 2
mdadm /dev/md0 --add /dev/sda1
mdadm /dev/md1 --add /dev/sda2
mdadm /dev/md2 --add /dev/sda3

If you chose option 2 and your drives now have a different ordering, swap “/dev/sda” and “/dev/sdb” everywhere above.

The RAID array will now rebuild. To check its progress:

cat /proc/mdstat

Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md0 : active raid1 sdb1[1] sda1[0]
      9767424 blocks [2/2] [UU]

md1 : active raid1 sdb1[1] sda1[0]
      1951808 blocks [2/2] [UU]

md2 : active raid1 sdb2[2] sda2[0]
      68693824 blocks [2/1] [U_]
      [>....................]  recovery =  0.4% (16320/68693824) finish=22.4min speed=8160K/sec

unused devices:

Once the array is finished rebuilding, reinstall grub on the new drive. We’ll do both, for good measure.

grub-install /dev/sda
grub-install /dev/sdb

You should now be able to reboot without either drive, and your system will come up cleanly. If you ever need to replace a failed drive, remove it, use step 7 above to clone the partition scheme to the new drive and add it to the array.


If you are having issues with your RAID setup, especially if you have an older RAID setup or older release already, you might need these packages:

apt-get install lvm2 evms dmsetup

Tags: ,

  1. dk1’s avatar

    Aha – that fixed it! Thanks for your post! Saved me many headaches…


  2. Wes’s avatar

    sfdisk -d /dev/sda | /dev/sdb
    doesn’t work for me on CentOS 5.2
    sfdisk -d /dev/sda | sfdisk /dev/sdb
    works as expected


  3. Wes’s avatar

    Before mounting md0 and md2 and copying files to them
    they may need to be formatted (right after step 2)
    mkfs.ext3 /dev/md0; mkfs.ext3 /dev/md2

    For impatient copying in step 3 can be shortened to:
    cp -ax / /mnt
    cp -ax /home /mnt/home
    This will preserve directories used for mounting like mnt, sys, proc, cdrom, …


  4. tyler’s avatar

    Fixed the sfdisk line, Wes. Thanks.

    Regarding the cp, that assumes that the directories used for mounting like /dev, /mnt, /var/lock, etc are tmpfs. That is true for Ubuntu but not all distributions. Just running the cp -ax like that may copy the contents of those directories. Hence the cautious rsync approach.


  5. maddog737’s avatar

    Same setup (Ubuntu 8.04), but my problem for the past few days was 2-fold:

    1st at the end of step 4, grub-install didn’t work (hung), so I manually ran grub and entered:
    device (hd1) /dev/sdb
    root (hd1,0)
    setup (hd1)

    worked, but then on reboot at step 7 and selecting the second drive as the boot drive through the BIOS, the boot process would hang, dropping me to initramfs. At this point, I could mount /dev/md0 by

    mdadm -A /dev/md0 /dev/sdb1

    for each RAID partition, then exit from initramfs. Everything would boot then. After too many attempts at resolving this, I found that the problem was resolved by allowing the boot sequence to drop to initramfs, and enter

    mdadm -As –homehost=” –auto=yes –auto-update-homehost

    exit initramfs and allow the boot to complete. Reboot once (or twice), and everything works. From what I understand (noob here), when the RAID1 was created, the homehost= in mdadm.conf used by mdadm during the boot process didn’t match what was in the properties written to the RAID partition when it was created resulting in arrays not being mounted automatically. Several days of debugging were summarized in that simple line…

    That, and to read about the problem with degraded RAID arrays here:


  6. Ioannis’s avatar

    Marvelous article. Compact and with rich information.
    Unfortunately I have the most weird problem (in 8.04 server):
    After creating the raid arrays, rebooting successfully growing the raid (1 for me) arrays to include the second (sdb1, sdb2 etc…) devices, the system cannot boot (md devices are stopped during boot). It might have something to do with the order the modules are loaded (the sda and sdb sit in different controllers with different drivers), but it might have something to do with a mix in md arrays and sd devices. For example I have sda9-sdb9 that belong to md6 but the mdadm reports for the sda member:
    mdadm -E /dev/sda9
    Magic : a92b4efc
    Version : 00.90.00
    UUID : 61b6692d:3900807a:5e76b0e2:85a6fbc1 (local to host TransNetStreamer)
    Creation Time : Sat Jan 10 17:13:51 2009
    Raid Level : raid1
    Used Dev Size : 9735232 (9.28 GiB 9.97 GB)
    Array Size : 9735232 (9.28 GiB 9.97 GB)
    Raid Devices : 2
    Total Devices : 1
    Preferred Minor : 6

    Update Time : Sun Jan 11 20:15:26 2009
    State : clean
    Active Devices : 1
    Working Devices : 1
    Failed Devices : 1
    Spare Devices : 0
    Checksum : bb676a86 – correct
    Events : 0.760

    Number Major Minor RaidDevice State
    this 0 8 9 0 active sync /dev/sda9

    0 0 8 9 0 active sync /dev/sda9
    1 1 0 0 1 faulty removed
    while for the sdb member:
    mdadm -E /dev/sdb9
    Magic : a92b4efc
    Version : 00.90.00
    UUID : 61b6692d:3900807a:5e76b0e2:85a6fbc1 (local to host TransNetStreamer)
    Creation Time : Sat Jan 10 17:13:51 2009
    Raid Level : raid1
    Used Dev Size : 9735232 (9.28 GiB 9.97 GB)
    Array Size : 9735232 (9.28 GiB 9.97 GB)
    Raid Devices : 2
    Total Devices : 2
    Preferred Minor : 6

    Update Time : Sun Jan 11 15:22:22 2009
    State : clean
    Active Devices : 2
    Working Devices : 2
    Failed Devices : 0
    Spare Devices : 0
    Checksum : bb67209c – correct
    Events : 0.66

    Number Major Minor RaidDevice State
    this 1 8 25 1 active sync /dev/sdb9

    0 0 8 9 0 active sync /dev/sda9
    1 1 8 25 1 active sync /dev/sdb9

    different things. HOW IS THAT possible ?

    Again thanks for your time


  7. tyler’s avatar

    Yikes! I’ve never seen two parts of a RAID array show different results! If you solve this, please post it here.


  8. tyler’s avatar

    Correction: the list of devices in the superblock can not match whenever the partitions are not actually in the array. I had a machine showing this problem until recently, but I can’t say how it came about. I just re-added the affected partition to the array and it resolved itself.


    mdadm –detail /dev/md6
    mdadm -E /dev/sda9
    mdadm -E /dev/sdb9

    If sdb9 still shows bad superblock data, I’d suggest removing it from the array and re-adding it.


  9. wil’s avatar


    Thanks for this document. I agree with Wes that it is best to format your disk right after step 2 if it already has data on it. I neglected to do that and on reboot it gave me this error:

    The filesystem size (according to the superblock) is nnn blocks
    The physical size of the device is yyy blocks
    Either the superblock or the partition table is likely to be corrupt!

    Of course this makes perfect sense as now both the original partition and the raid disk had their own superblocks on there. Formatting the md(x) partitions and rerunning the rsync solved that.


  10. tyler’s avatar

    Thanks to several of you for pointing out the need to create filesystems on the new RAID partitions. I’ve edited the article to reflect that in step 2.


  11. Mudgen’s avatar

    What a great post! I’m actually familiar with all the pieces, but it’s terrific to have them put together in a road map.
    Surprised the original Centos poster did not call out that the update-initramfs equivalent on Redhat/Centos/Fedora would be mkinitrd.


  12. tyler’s avatar

    Hi Mudgen,

    What’s the exact command with mkinitrd? Any switches? It would be good to have it here.


  13. Don Radick’s avatar

    Thanks for the very informative guide!
    I recently had to move my root file system from one pair of Raid1 disks to another pair of Raid1 disks, and was totally non-plussed to find that although grub appeared to be working, I would get dumped into a BusyBox prompt by initramfs.
    Although the BusyBox prompt didn’t say, I found I could run mdadm from there, and found that the UUID of the Raid1 filesystem was different from the new one I had prepared.
    After a bit of googing, I found this page which pointed me in the direction of a fix.
    Using your chroot method and update-initramfs worked like a charm.

    gracia amigo.


  14. kjw’s avatar

    rather than rsync, I recommend dump. It’ll properly transfer everything on your disk, like extended security attributes, and hard linked files, and automatically avoid anything weird. Just precede this with a mkfs, and you can be sure that everything is clean (dump|restore does not delete files, only add them)

    cd /
    dump -0 -f – / | (cd /mnt && restore -rf -)


    1. Tyler Wagner’s avatar

      Thank you for the tip, Kevin. You are correct; my procedure isn’t concerned with hard links, extended attributes, or ACLs. Add “-HXA” to rsync to get them, but it will be slower. My exclusions list avoids the expected locations of weird things, but it would be bad if someone mounted a drive in an unexpected place.

      The reason I use rsync is so that I can run it multiple times, right up until the switchover, for minimum downtime and no loss of data between when the copy is run, and swapping over. My procedure can be run on a live system right up until the final rsync.

      I’m amused to see that dump is no longer installed by default on Ubuntu.


    2. WebDawg’s avatar

      A gem among the internet sir. I am going to clone this on my wiki for personal storage (with a link to this site!) but this saved me alot of time.

      The newer grub has a different file though. grub.cfg if I remember.

      Still. Perfect.


      1. Tyler Wagner’s avatar

        Excellent. Perhaps you’d be so kind as to write updated commands for Grub 2? I’ll edit the post to include them.


      2. WebDawg’s avatar


        Edit /boot/grub/menu.list and find the line like this:

        # kopt=root=UUID=9e299378-de65-459e-b8b5-036637b7ba93 ro

        Replace the UUID with the one you just found. Leave the line commented, and save the file. Now rebuild menu.lst to use the new UUID:

        You want to edit the /boot/grub/grub.cfg and replace the many UID entries there instead.

        I may still keep the old instructions for the old grub though?


        1. Tyler Wagner’s avatar

          I’ve updated the guide to support GRUB 1 and 2. Thanks.


        2. Matt Hare’s avatar

          Great article! Followed it step by step and am now watching the array build onto the new drive, hopefully after this we can boot and the system will come up clean. Thanks again for the excellent tutorial!


        3. Anders’s avatar

          Great guide! Thanks.
          One thing that happend to me was that I got an error message when copying .gvfs in home directory. I incuded /home/*/.gvfs/ in the filter list and all went well (Ubunti 10.04 LTS)


          1. Tyler Wagner’s avatar

            Thanks, Anders. I’ll add that exclusion. I had never considered performing this while logged in at the desktop.


          2. VIKAS’s avatar

            Excellent article, each point is explained nicely. I was able to mirror my RHEL 6.2 OS disks on the very first go. Many thanks for your efforts to write this article.

            The only thing which I did not understand is why names of my RAID devices keeps on changing after reboots. Earlier they were,

            /dev/md0 – /
            /dev/md1 – /home
            /dev/md2 – swap

            After reboot for some strange reasons

            /dev/md127 – /
            /dev/md126 – /home
            /dev/md125 – swap

            The order (125, 126, 127) keeps on changing after each reboot.

            Any ideas to overcome this ?


            1. Tyler Wagner’s avatar

              MD raid arrays are auto-detected and named at boot time. Try defining them in /etc/mdadm/mdadm.conf (on Debian, should be similar on Red Hat).


            2. vikas’s avatar

              I did the same with no luck :(


              1. Tyler Wagner’s avatar

                It seems to be /etc/mdadm.conf on RHEL 6. Beyond that, I’m afraid I have no advice.


              2. Cab’s avatar

                Thanks for this article! I have been working on moving over to a raid1, and have just almost gotten it working. I’m so close I can taste it. The machine will now boot from the raid, but I am trapped at the login screen. After entering my password, I just get dumped back to the login screen again, whether I try to login as my admin or regular account. I can only login as a guest. The original HDD is not part of the array, so I can switch back to it easily. On the old setup it logs in automatically, so I don’t know why the new setup is not doing the same, since all the files/settings should have copied over to the new drives, yes? Any suggestions would be greatly appreciated. I’m running Ubuntu 12.04. Thanks.


                1. Tyler Wagner’s avatar

                  Hi Cab,

                  I can’t see any reason why that would happen. I assume that something went wrong in the copy. Either something important was excluded, or file permissions don’t match before and after. But if you used “rsync -av” to a blank disk, I can’t see how the latter would happen.

                  Consider checking /var/log/syslog and /var/log/lightdm/lightdm.log. You’ll need sudo to read both.

                  Also try switching to a text console. At login window, press Ctrl-Alt-F1, and login there. Does it work, and do you have your files? Are your files encrypted with ecryptfs (you checked “encrypt my home directory” at installation).


                2. Cab’s avatar

                  Thanks, Tyler. Turns out it was a pretty easy fix… once I finally thought about it enough. I was moving from a 250GB HDD that had nothing except the OS on it onto two raid1-ed 2TB drives, on which is a 50GB /, 2GB swap, and remainder for /home. Because my old drive had no data or anything I used on it, I had not been running the rsync for the /home partition, because I had simply been thinking that would copy over data. Once I thought about it, I realized that not syncing the /home directory was preventing the log in from working, so I ran the rsync and now it works fine.

                  The only problem I’m having now is that it won’t automatically boot when the raid is degraded. I’ve tried a few things, and for some reason it goes to the purple screen, and if I just blindly type “y” or “reboot”, then it boots degraded and I can rebuild the array. I’ve seen some bug reports on that, and I can’t seem to get it to go away. But at least I know it will boot degraded, I just have to remember to type stuff at the purple screen, even though I can’t see it asking me if I want to boot degraded or see any screen activity when I type. While it’s annoying, I really don’t care because I know I can boot when/if one of the drives fails. So now I am good enough to start copying over my photo collection and other files, set up my backupping, and enjoy the security of the raid system.

                  Again, thanks for the writeup, once I actually followed the whole set of instructions, it worked great!


                  1. Tyler Wagner’s avatar

                    I’m glad I could help, Cab.

                    A lot of issues become apparent when you work outside the GUI. For instance, you can login from console without a home directory. The terminal will dump you in /, and print an error message. As for the degraded RAID issue, consider disabling splash. Just remove “quiet” from the default grub options, and you’ll have a useful boot/shutdown screen with technical details. You can also press ESC to do the same thing for just one boot (it toggles splash, so you can press repeatedly).

                    Did you install grub on both drives?


                    1. Cab’s avatar

                      Yes, I installed grub on both of the new drives. It’s just weird, it seems to be asking me for input, just not showing me anything except the “purple screen of death.” When I just type blindly, it boots fine. Frankly, at this point I’m okay with the fact that it works and since I leave it running all the time anyway, I’m not terribly concerned with knowing it has strange boot behavior. When a drive in the raid fails and I have to power down to replace it, I will just have to type “y” at the purple screen, and it should boot up fine. I may try disabling splash, but I’m not going to worry about spending too much time working on this issue since it’s working now. This is not my primary machine, I simply use it for file storage and will be driving my backup routine through it. I would feel differently and use it as the primary machine if Adobe would decide to release a version of Lightroom and Photoshop that ran natively in Linux (I’ve tried running Wine, it was not a satisfactory experience…), but until then, I’m afraid I’m stuck in Windows land for the time being.

                      Having a working raid for storage and a system that can handle backups is just what I need this machine to do, and thanks in large part to this writeup, that’s what I have!


                    2. JonH’s avatar

                      It is possible to create a degraded mirror, with one half missing by replacing a drive name with “missing”:
                      mdadm –create /dev/md1 –level=1 –raid-devices=2 /dev/sdb1 missing
                      instead of using –force, then mdadm can still warn/stop you if you’ve messed up somewhere in the command.


                      1. Tyler Wagner’s avatar

                        Ah, I did not know that. Thanks.


                      2. Jonb’s avatar

                        Thanks, great article.

                        I used a raid5 array as root directory “/” on Ubuntu 10.04 server, tried to upgrade to 12.04 but failed rendering an un-bootable system. I installed a new HD installed 12.04 on it while other disks where detached (just in case…) and thank God for the excellent mdadm programmers it found my raid5 array (I actually have a raid1 array as well on SSD disks, mdadm found that to :) ).
                        My problem is I would like to use the raid5 array as the root directory again (I don’t think my power supply is made for all the stuff I have in the box, so need to get rid of the disk again) but rsynk will delete the contents of the array and a backup will take forever.
                        Do you know a solution that will preserve other content of the raid ?



                        1. Tyler Wagner’s avatar

                          Hi Jon,

                          rsync will do exactly what you tell it to do. It will duplicate your data or overwrite it, depending on how you invoke it. If you don’t want it to delete the contents of the RAID, play with the rsync options (always with -n first!) until you’re sure it will do what you want.


                        2. Andrey’s avatar

                          Thank you very much for the article. It gave me a clear insight and basis to develop my Linux administration techniques.



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