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I am having trouble going from a single disk to raid 10

The command issued is:

mdadm --create /dev/md0 --level=10 --raid-devices=8 /dev/sd[abcdefgh]1

The output is:

mdadm mdadm: cannot open /dev/sda1: Device or resource busy

I have verified this has nothing to do with DM:

]# dmsetup status

No devices found

The file system is GPT, I used sgdisk --backup=table /dev/sda follwoed by sgdisk --load-backup=table /dev/sdb through to sdh to copy the partitions table

the table looks like:

Number  Start   End     Size    File system     Name  Flags
 1      1049kB  525MB   524MB   ext3                  boot
 2      525MB   86.4GB  85.9GB  ext4
 3      86.4GB  90.7GB  4295MB  linux-swap(v1)
 4      90.7GB  1000GB  909GB

I have created the other arrays fine however I cannot create the raid for the 1st and 2nd partition.

current status:

]# cat /proc/mdstat
Personalities : [raid10]
md3 : active raid10 sdh3[7] sdg3[6] sdf3[5] sde3[4] sdd3[3] sdc3[2] sdb3[1] sda3[0]
      16766976 blocks super 1.2 512K chunks 2 near-copies [8/8] [UUUUUUUU]

md4 : active raid10 sdh4[7] sdg4[6] sdf4[5] sde4[4] sdd4[3] sdc4[2] sdb4[1] sda4[0]
      3552147456 blocks super 1.2 512K chunks 2 near-copies [8/8] [UUUUUUUU]
      [========>............]  resync = 42.5% (1513033344/3552147456) finish=76.2min speed=445722K/sec

unused devices: <none>

Can anyone offer any advice, do I need to boot in to a rescue disk and create the arrays for / and /boot while they are not mounted?

share|improve this question
You are likely trying this in a running system while /dev/sda1 is mounted. Naturally, this can't work, also things are a lot more complicated than just to convert the partitions into a RAID (you need to update the initramfs, the boot loader and /etc/fstab). If you don't understand this, you shouldn't continue before reading up on this matter. – Sven Apr 13 '13 at 13:58
up vote 1 down vote accepted

do I need to...create the arrays for / and /boot while they are not mounted?


I hope you also realised that the old contents will be wiped in the process, so you might want to create a new array with one device missing (use mdadm --level=10 --raid-devices=8 --missing /dev/sdb1 /dev/sdc1 /dev/sdd1 /dev/sde1 /dev/sdf1 /dev/sdg1 /dev/sdh1). Then format the filesystem on the new array volume and copy all data from /dev/sda1 to it. Then reboot from the array (thus NOT using the /dev/sda1 root) and actually add /dev/sda1.

Do not forget to adjust the bootloader accordingly.

share|improve this answer
Ah ok thanks, usually I would not be doing it this way at all, the server was taken on with 8 drives with the OS on 1 disk only and the others untouched, it might be worth just setting it up again from scratch with the KVMoIP I suppose. I thought it may have been an option to simply dd sda1 and sda2 over to sd[bcdefgh]1 and sd[bcdefgh]2 then create the arrays even with sda1 and sda 2 mounted, I suppose I could still try that with sda1,2 missing then add them to the arrays in resuce mode unmounted but if that is going to wipe everything I might as well just reinstall. – Backtogeek Apr 13 '13 at 14:36
Ubuntu is not CentOS, but it is close enough that several of the answers on A.U. also apply. Exaples: (In your case it is RAID 10 and not RAID5, but the idea is the same: Create the new array and format it, copy data, fix bootloader to boot from the RAID, test, add old partition to the RAID (thus loosing the old content on it). – Hennes Apr 13 '13 at 14:51
There was enough information in that link to give me the answers and order of things I needed all sorted now and booting+running on raid 10 Thanks. – Backtogeek Apr 13 '13 at 16:22

Just try to stop before reassambling array :

sudo mdadm -Esv
sudo mdadm  --stop /dev/md*
sudo mdadm --misc --scan --detail /dev/md0
sudo mdadm -v --assemble "$array" "$disk1$part" "$disk2$part"
share|improve this answer

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