Resize/Shrink Software RAID1 FileSystem/Volume/Partition and setup a LVM on the free disk space created
This guide on how to resize a software raid1 should work on most Linux Distributions. I used a dedicated server located in Strassburg running Ubuntu Server 12.04, and I connected to it via ssh from Asia. 
Here my setup prior to doing this:
Two 2 TB hard disks (sda/sdb) with 3 partitions each
sda1/sdb1 -- md0 -- /boot
sda2/sdb2 -- md1 -- swap
sda3/sdb3 -- md2 -- /
md2 uses pretty much all the space.
Here the setup after completing the steps below:
Two 2 TB hard disks (sda/sdb) with 4 partitions each
sda1/sdb1 -- md0 -- /boot
sda2/sdb2 -- md1 -- swap
sda3/sdb3 -- md2 -- / (~320GB)
sda4/sdb4 -- md3 -- LVM "nova-volumes" (~1650GB)
Make sure you got the needed packages installed:
# sudo apt-get install lvm2 dmsetup mdadm
Boot the server in recover mode, then do:
# sudo -s -H
# mdadm -A --scan
mdadm: /dev/md/1 has been started with 2 drives.
mdadm: /dev/md/2 has been started with 2 drives.
We have 3 raid partitions, md2 is the one we need to resize.
Make sure it is the correct partition:
# fdisk -l /dev/md2
2 heads, 4 sectors/track, 485686238 cylinders, total 3885489904 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disk identifier: 0x00000000
Disk /dev/md2 doesn't contain a valid partition table
Almost 2TB looks good.
You may have to unmount the RAID partition:
# umount /dev/md2
Set md2 as faulty on sda. The 3rd partition is sda3 while the 3rd RAID volume is md2, thanks to some geeks that can't agree whether an array starts with a zero or a 1…. anyways:
# mdadm --manage /dev/md2 --fail /dev/sda3
Remove the partition from the array:
# mdadm --manage /dev/md2 --remove /dev/sda3
This will prevent any possible sync to start while we work on the filesystem etc.
We will also need to repartition sda3, so it needs to be out of the RAID array.
Reduce the size of the RAID filesystem for md2, for now to 280GB so it fits in the
later resized RAID volume:
# e2fsck -f /dev/md2
# resize2fs -f /dev/md2 280G
The filesystem on /dev/md/2 is now 73400320 blocks long.
Reduce the size of the RAID volume to 305GB, so it will fit in the new 320 GB partition later.
To get the right size do 305x1024x1024 = 319815680.
# mdadm --grow /dev/md2 --size=319815680
Delete the sda3 partition and recreate it with the size of 320GB. I used cfdisk for this, which is
pretty much self explanatory… , there is also plenty of help on deleting/creating partitions.
# cfdisk
I set the partition type to FD (Linux Raid autodetect) and the size to 343599 MB, which is
slightly bigger than the RAID filesystem would be when set to 320GB.
Add the new 320GB partition to the array, and let it synchronize.
# mdadm --manage /dev/md2 --add /dev/sda3
mdadm: not performing --add as that would convert /dev/sda3 in to a spare.
mdadm: To make this a spare, use "mdadm --zero-superblock /dev/sda3" first.
Do this:
# mdadm --zero-superblock /dev/sda3
and then again:
# mdadm --manage /dev/md2 --add /dev/sda3
You may have to do the same for sdb3 later.
Watch the sync progress, as you got to waaaaaaaiiiiiit for it to finish:
# watch cat /proc/mdstat
319815680 blocks super 1.2 [2/1] [_U]
[==>………………] recovery = 14.7% (47026560/319815680) finish=43.0min speed=111643K/sec
Press Ctrl+c to stop watching it…
Once the sync is done, it should look like this:
# cat /proc/mdstat
md2 : active raid1 sda3[2] sdb3[1]
319815680 blocks super 1.2 [2/2] [UU]
md1 : active raid1 sda2[0] sdb2[1]
9999288 blocks super 1.2 [2/2] [UU]
md0 : active raid1 sda1[0] sdb1[1]
766964 blocks super 1.2 [2/2] [UU]
Next step is to set md2 as faulty on sdb3:
# mdadm --manage /dev/md2 --fail /dev/sdb3
Remove the drive from the array:
# mdadm --manage /dev/md2 --remove /dev/sdb3
Delete the sdb3 partition and recreate it with the size of 343599 MB to match sda3.
# cfdisk /dev/sdb
Add the new partition to the array, and let it synchronize.
# mdadm --manage /dev/md2 --add /dev/sdb3
Watch the sync progress, as you got to wait for it to finish, agaaaaaaaiiiin:
# watch cat /proc/mdstat
Press Ctrl+c to stop watching it…
Once the sync is done, it should look like this:
# cat /proc/mdstat
md2 : active raid1 sda3[0] sda3[1]
327155712 blocks super 1.2 [2/2] [UU]
md1 : active raid1 sda2[0] sdb2[1]
9999288 blocks super 1.2 [2/2] [UU]
md0 : active raid1 sda1[0] sdb1[1]
766964 blocks super 1.2 [2/2] [UU]
Make sure the new partition size is recognized:
# blockdev –rereadpt /dev/sda
# blockdev –rereadpt /dev/sdb
Make the RAID volume use up the maximum space on the partition:
# mdadm --grow /dev/md2 --size=max
Run a file system check:
# e2fsck -f /dev/md2
Increase the size of the filesystem to take up all the space of the volume:
# resize2fs -f /dev/md2
The filesystem on /dev/md/2 is now 83887157 blocks long.
Check the filesystem
# e2fsck -f /dev/md2
Do not reboot yet, if you are going to setup the LVM as well, just continue below.
Use the newly available space to setup another RAID array for LVM.
Start with setting up the LVM for nova, by creating the partitions for md3 on both drives:
# cfdisk /dev/sda
# cfdisk /dev/sdb
I set the partitions up to use the maximum space available.
Check if all partitions are OK
# fdisk -l /dev/sda /dev/sdb
/dev/sda1 2048 1535999 766976 fd Linux raid autodetect
/dev/sda2 1536000 21536767 10000384 fd Linux raid autodetect
/dev/sda3 21536768 692636077 335549655 fd Linux raid autodetect
/dev/sda4 692636078 3907029167 1607196545 fd Linux raid autodetect
Partition 4 does not start on physical sector boundary.
Device Boot Start End Blocks Id System
/dev/sdb1 2048 1535999 766976 fd Linux raid autodetect
/dev/sdb2 1536000 21536767 10000384 fd Linux raid autodetect
/dev/sdb3 21536768 692636077 335549655 fd Linux raid autodetect
/dev/sdb4 692636078 3907029167 1607196545 fd Linux raid autodetect
Partition 4 does not start on physical sector boundary.
Create the new array with one drive:
# mdadm --create /dev/md3 --level=1 --raid-devices=2 /dev/sda4 missing
Add sdb4 to the array
# mdadm --manage --add /dev/md3 /dev/sdb4
Make md3 a LVM volume
# pvcreate /dev/md3
Add the new volume to the "nova-volumes" group
# vgcreate nova-volumes /dev/md3
I had to reassemble the array while creating this tutorial, which resulted in a broken grub due to a change of the UUID of the md2 array, on top of that I couldn't do chroot, so manual patching had to be done.
Only do these steps, if you can't boot normally, or know for a fact that you reassembled your raid array(s).
Update mdadm.conf and grub.cfg, but first get the UUIDs:
# blkid
/dev/sda2: UUID="42679326-1f8a-b1e6-fa6e-6c3777a5caf8" UUID_SUB="bdc9307d-0d92-5062-a04d-41a48a8a2c60" LABEL="puck538:1" TYPE="linux_raid_member"
/dev/sda3: UUID="443dbe36-1d80-5344-3989-4c73f56e7dd2" UUID_SUB="42a10b71-9bd6-11a4-517d-b198858e8b06" LABEL="puck538:2" TYPE="linux_raid_member"
/dev/sda4: UUID="c0c5c51e-5956-3116-6fee-ccd193564574" UUID_SUB="08698000-adab-10a1-da9d-7209707a5776" LABEL="puck538:3" TYPE="linux_raid_member"
/dev/sdb1: UUID="5910cbc1-0b5c-044c-b286-f447ab78e5d9" UUID_SUB="626284bb-c30c-8474-1f8f-f756b62a2814" LABEL="puck538:0" TYPE="linux_raid_member"
/dev/sdb2: UUID="42679326-1f8a-b1e6-fa6e-6c3777a5caf8" UUID_SUB="9ddfd438-7e6c-9181-1499-13a29c42adc3" LABEL="puck538:1" TYPE="linux_raid_member"
/dev/sdb3: UUID="443dbe36-1d80-5344-3989-4c73f56e7dd2" UUID_SUB="099d4e22-03c0-1d4b-3d15-64f396a84d36" LABEL="puck538:2" TYPE="linux_raid_member"
/dev/sdb4: UUID="c0c5c51e-5956-3116-6fee-ccd193564574" UUID_SUB="fa918a45-47c4-6444-e912-16951f2191a0" LABEL="puck538:3" TYPE="linux_raid_member"
/dev/md0: UUID="5c6eb879-6d96-487f-8523-90c40ee21a3e" TYPE="ext2"
/dev/md1: UUID="f92ff19b-aee4-4a94-a225-df1d6a2454b0" TYPE="swap"
/dev/md2: UUID="e06f4042-f285-4cf8-846b-59539d6b00ac" TYPE="ext4"
/dev/md3: UUID="LRX6l7-mOSx-TOm6-nq9M-CUKt-Vrem-YivLWw" TYPE="LVM2_member"
# mkdir /md0
# mount /dev/md0 /md0
# nano /md0/grub/grub.cfg
search for the first "set root" and update the UUID to the new one you see behind /dev/sda3: and /dev/sdb3:
you have to delete the dashes in the UUID, so it becomes one long string.
/dev/sda3: UUID="443dbe36-1d80-5344-3989-4c73f56e7dd2" becomes "443dbe361d80534439894c73f56e7dd2"
OLD: set root='(mduuid/297096e0a18b36c10f1c40c0bdd4225b'
NEW: set root='(mduuid/443dbe361d80534439894c73f56e7dd2)'
Mount / (md2) and update the UUID for md2 in mdadm.conf, also add md3 to the list
# mkdir /md2
# mount /dev/md2 /md2
# nano /md2/etc/mdadm/mdadm.conf
/dev/sda3: UUID="443dbe36-1d80-5344-3989-4c73f56e7dd2" becomes "443dbe36:1d805344:39894c73:f56e7dd2"
/dev/sdb4: UUID="c0c5c51e-5956-3116-6fee-ccd193564574" becomes "c0c5c51e:59563116:6feeccd1:93564574"
ARRAY /dev/md/0 metadata=1.2 UUID=5910cbc1:0b5c044c:b286f447:ab78e5d9 name=yourhost:0
ARRAY /dev/md/1 metadata=1.2 UUID=42679326:1f8ab1e6:fa6e6c37:77a5caf8 name=yourhost:1
ARRAY /dev/md/2 metadata=1.2 UUID=443dbe36:1d805344:39894c73:f56e7dd2 name=yourhost:2
ARRAY /dev/md/3 metadata=1.2 UUID=c0c5c51e:59563116:6feeccd1:93564574 name=yourhost:3
Note: "yourhost" needs to be replaced by your hostname…
Done, time to reboot!
Note: You may have to add the new array after reboot. Just run this once to make sure it is added:
# mdadm -A --scan
Enjoy 
References & Resources:
http://www.howtoforge.com/how-to-resize-raid-partitions-shrink-and-grow-software-raid
http://www.evilbox.ro/linux/ubuntu-raid1-resize/
http://mkfblog.blogspot.com/2007/11/resizing-raid1-system-partition.html
http://lavezarez.blogspot.com/2011/01/raid-1-not-starting-and-mounting-on.html
https://help.ubuntu.com/community/Installation/RAID1+LVM
https://raid.wiki.kernel.org/index.php/Partitioning_RAID_/_LVM_on_RAID
16213
Do NOT run mdadm –grow /dev/md2 –size=max. Instead, resize to your destination size.
I see no reason not to use –size=max
“The size can be given as max which means to choose the largest size that fits on all current drives.”
– http://linux.die.net/man/8/mdadm
Great article, thank you.
Have you tried
blockdev –rereadpt /dev/sdb
blockdev –rereadpt /dev/sda
after the cfdisk? Might stop that jumping up to the previous max size?
Great tuto !
Would you mind if I translate it to french and post it on my blog ? Of course, you’ll be quoted as the original author.
Of course you can!
A link back to this post would be great!
You can also post the link to your translation, once you have done it, so french speaking people can go to your blog
Hi,
I am really a newbie using linux. So I want to learn by trying out some stuff. I have a similar server setup as in the example.
I am trying your guide but I can’t manage to finish it. I am running into some problems.
I am also having the problem that the raid array by using the grow to maximum size command grows to the original size.
I tried removing the array and recreating one, but than I got errors with different physical size and superblock size or something like that.
I will try again without using the grow to max but by giving the exact size of the /dev/sda3 partition. Is that ok?
Another strange thing I ran into was that after resizing the md2 array, the server wouldn’t boot anymore (although the UUID was not changed). When deleting the sda3 partition with cfdisk it said that there was no partition which was set to bootable. Could that be the problem? Strange thing is that when I cfdisk before changing anything, there is also no partition that had a bootable flag.
I also ran into problems creating the new /dev/sda4 partition. Using cfdisk I could make a new partition. But the partition was not recognized. Looking back, this could be due to the growing back to original size of the md2 array…
What’s the reason for using different sizes for the partition and the array and afterwards let the array grow to the size of the partitions? Has this something to do with the synchro between the two partitions? Or can I use the same size immediately?
Kind Regards and thanks for the guide! I hope I can succeed one day.
Hello,
the comment section is not really a good place to discuss this in details.
If the file system grows to the original size, then you encountered the same thing that happened to me one time. Look at the orange bordered box near that step, I also provided my solution at the bottom of the post.
Growing the file system to fit the new partition size avoids having a file system that does not fit inside the resized partition, while guaranteeing that the file system uses the maximum space available.
Is there another way how I can contact you? I suppose you have my mail address from my post.
I am still having some problems and I wanted to ask you a thing or two.
Can you send me an e-mail?
Thanks
helped a lot!
Personally i ran into trouble with this article and lost my data
You do not explain precisely “Delete the sda3 partition and recreate it with the size of 320G”. Personally i used fdisk and use a Begin sector different from the original one (error, mistake,.. ?)
Then you don’t mention md superblock metadata version. For me the ancient one was Metadata Version 0.90. Using Knoppix 7.6 made me use by default Metadata Versiuon 1.2.
I don’t know why but the result is malfuntionning..
For later viewers i will add some pieces which could help
I did thisq resize on /dev/md1 (sda2 and sdb2) and had no more /dev/md1 (/) so server not booting
With Knoppix i recreated md1 which had disappeard
mdadm –create –verbose –level=1 –metadata=0.9 /dev/md1 –raid-devices=2 /dev/sda2 /dev/sdb2
Made faulty and remove /dev/sda2
With fdisk delete and recreate sda2 with first sector original (type fd)
Add /dev/sda2
Made faulty and remove /dev/sdb2
With fdisk delete and recrete sdb2 with first sector original (type fd)
Add /dev/sdb2
After reboot s
Server boots well and i can find my data back
…
beware if typos!
Thanks for the comment and warning.
They are not typos, WP just auto-formatted the lines. I need to add a code wrapper, so it doesn’t happen anymore.