Disassemble a RAID 1 arragement without removing/reinstalling the system

Question

I've set up a Soft Raid 1 using Debians built in RAID systems. I set up the raid because I had a space HDD when I set up the server and thought why not. The RAID is set up using what-ever Debian did when I installed the OS (sorry, not a linux techie).

Now, how-ever I could really use the disk for a much more useful purpose.

Is it easy to discontinue the raid without having to reinstall the OS, and how would I go about doing this?

fdisk -l

Disk /dev/sda: 500.1 GB, 500107862016 bytes
255 heads, 63 sectors/track, 60801 cylinders, total 976773168 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: 0x000d9640

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1            2048   976771071   488384512   fd  Linux raid autodetect

Disk /dev/sdb: 500.1 GB, 500107862016 bytes
255 heads, 63 sectors/track, 60801 cylinders, total 976773168 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: 0x0009dd99

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1            2048   950560767   475279360   83  Linux
/dev/sdb2       950562814   976771071    13104129    5  Extended
Partition 2 does not start on physical sector boundary.
/dev/sdb5       950562816   976771071    13104128   82  Linux swap / Solaris

Disk /dev/sdc: 2000.4 GB, 2000398934016 bytes
255 heads, 63 sectors/track, 243201 cylinders, total 3907029168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x6fa10d6b

   Device Boot      Start         End      Blocks   Id  System
/dev/sdc1              63  3907024064  1953512001    7  HPFS/NTFS/exFAT

Disk /dev/sdd: 7803 MB, 7803174912 bytes
122 heads, 58 sectors/track, 2153 cylinders, total 15240576 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0xc3072e18

   Device Boot      Start         End      Blocks   Id  System
/dev/sdd1   *        8064    15240575     7616256    b  W95 FAT32

fstab content:

# /etc/fstab: static file system information.
#
# Use 'blkid' to print the universally unique identifier for a
# device; this may be used with UUID= as a more robust way to name devices
# that works even if disks are added and removed. See fstab(5).
#
# <file system> <mount point>   <type>  <options>       <dump>  <pass>
# / was on /dev/sdb1 during installation
UUID=cbc19adf-8ed0-4d20-a56e-13c1a74e9cf0 /               ext4    errors=remount-ro 0       1
# swap was on /dev/sdb5 during installation
UUID=f6836768-e2b6-4ccf-9827-99f58999607e none            swap    sw              0       0
/dev/sda1       /media/usb0     auto    rw,user,noauto  0       0
/dev/sdc1       /media/mns       ntfs-3g defaults        0       2

Solution 1

The easiest method, that requires no changes to your setup whatsoever, is probably to reduce the RAID to a single disk. That leaves you the option to add a disk and thus re-use the RAID at a later time.

mdadm /dev/mdx --fail /dev/disky1
mdadm /dev/mdx --remove /dev/disky1
mdadm --grow /dev/mdx --raid-devices=1 --force

The result would look something like this:

mdx : active raid1 diskx1[3]
      62519296 blocks super 1.2 [1/1] [U]

Ta-daa a single disk "RAID1".

If you want to get rid of the RAID layer altogether, it would involve mdadm --examine /dev/diskx1 (to find out the data offset), mdadm --zero-superblock (to get rid of the RAID metadata), and parted to move the partition by the data offset so it points to the filesystem, and then update bootloader and system configs to reflect the absence of RAID...

Solution 2

Just fail and remove one of your drives:

mdadm /dev/md0 --fail /dev/sdb --remove /dev/sdb

After that change your /etc/fstab to use the drive left in RAID.

Reboot. And then destroy your RAID:

mdadm /dev/md0 --destroy

Have fun :)

Comments

[Gilles 'SO- stop being evil']

The output from fdisk isn't consistent with your having a RAID1 volume. It's possible to have partitions with an incorrect type, but even then partition sizes don't match. Post the output of cat /proc/mdstat, cat /proc/partitions, cat /proc/mounts, vgs and cat /sys/block/dm-*/dm/name (I think that should let us conclusively determine what all your disks are being used for).

[webknjaz]

And also, please, post output of lsblk - it will print a good representation of your block devices layout including device-mapper ones. And also tell us which devices you think could be united in RAID and what mountpoint (you think) RAID partition is mounted to.

[Jonas Laursen]

I dont have any drives mounted as md0... My fsdisk -l pastebin.com/uFYmShmT - All I know is that it is one of the 500 gb drives that I need to disconnect.

[Jonas Laursen]

The thing is, i did not use this mdadm program to create the raid. Infact, I've just installed it, and it says there are no raids?

[frostschutz]

If you're not using mdadm Software RAID, you should be more specific in your question.

[fpmurphy]

Looking at the fdisk output you provided, there is only one partition marked fd. So I do not think RAID 1 is set up and running on your system.

[webknjaz]

I only see /dev/sda being marked as RAID. Please answer questions under original post.