How-to Remove RAID Devices

Continuing with our Linux RAID How-to series, in this KB, we will show you how to remove a Linux software RAID device.

Typically, we remove devices from a RAID array because we want to re-purpose the device(s) for other use.  Removing a device from an array is destructive and will destroy the entire array so proceed with caution.

Note: If you are trying to remove a failed device from an array, see our Removing Failed RAID Devices KB.

1. Backup your data!  Ensure you have a full backup of your data before proceeding.  Any data on the array will be lost once we remove a device from the array.
   
   
2. If the array is mounted, unmount the array before proceeding
   
   

   [root@Linux01 TCPDumpLV]# df -kh Filesystem Size Used Avail Use% Mounted on /dev/mapper/VolGroup00-LogVol04 3.9G 2.2G 1.6G 59% / /dev/sda1 99M 12M 82M 13% /boot tmpfs 1006M 0 1006M 0% /dev/shm /dev/mapper/VolGroup00-LogVol00 992M 41M 901M 5% /home /dev/mapper/VolGroup00-LogVol02 992M 69M 872M 8% /tmp /dev/mapper/VolGroup00-LogVol03 2.0G 152M 1.7G 9% /var /dev/md0 7.9G 147M 7.4G 2% /RAID5

   Note: You can see /dev/md0 is mounted on /RAID5
   
   

   [root@Linux01 ~]# umount /dev/md0 [root@Linux01 ~]#

   
   
3. Note the devices that make-up the array
   
   

   [root@Linux01 ~]# mdadm --detail /dev/md0 /dev/md0: Version : 00.90.03 Creation Time : Mon Jun 15 14:28:48 2009 Raid Level : raid5 Array Size : 8385664 (8.00 GiB 8.59 GB) Used Dev Size : 4192832 (4.00 GiB 4.29 GB) Raid Devices : 3 Total Devices : 3 Preferred Minor : 0 Persistence : Superblock is persistent : Update Time : Mon Jun 15 15:26:40 2009 State : clean Active Devices : 3 Working Devices : 3 Failed Devices : 0 Spare Devices : 0 : Layout : left-symmetric Chunk Size : 64K : UUID : 9a37eac9:0525c02f:cf141ece:af0de2a7 Events : 0.2 Number Major Minor RaidDevice State 0 8 17 0 active sync   /dev/sdb1 1 8 33 1 active sync   /dev/sdc1 2 8 49 2 active sync   /dev/sdd1

   Note: /dev/sdb1, /dev/sdc1 and /dev/sdd1 makeup /dev/md0
   
   
4. Stop the array
   
   

   [root@Linux01 /]# mdadm -S /dev/md0 mdadm: stopped /dev/md0 [root@Linux01 /]#

   
   
5. Zero out each of the superblock's of the devices that belongs to the RAID array
   
   

   [root@Linux01 /]# mdadm --zero-superblock /dev/sdb1 [root@Linux01 /]# mdadm --zero-superblock /dev/sdc1 [root@Linux01 /]# mdadm --zero-superblock /dev/sdd1 [root@Linux01 /]#

   Note: Zeroing the superblocks will destroy all the data on the array
   
   
6. Remove the  DEVICE and ARRAY entry's associated with the array from /etc/mdadm.conf
   
   

   DEVICE /dev/sdb1 /dev/sdc1 /dev/sdd1 ARRAY /dev/md0 level=raid5 num-devices=3 devices=/dev/sdb1,/dev/sdc1,/dev/sdd1

   
   
7. Remove the array from /etc/fstab
   
   

   /dev/md0 /RAID5 ext3 defaults 0 0

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Chris Edwards  - fstab |26/09/2009 04:54:30 Can I add one of the drives back into fstab after step 7. and boot off of it? Do I need to reinstall GRUB? Thanks! Chris Reply | Quote

thirt |28/09/2009 09:41:47 Hi Chris, There would certainly be nothing preventing you from adding another device to the fstab. I'm not sure entirely what you are attempting to do, but you don't necessarily have to install grub on the new device to boot from it. Assuming you already have a /boot filesystem that contains your kernel initrd etc., so long as your new RAID device contains your system files, you could just add another entry in your grub.conf to be a target for your root filesystem. Hope that helps. Tom Reply | Quote

Chris Edwards |28/09/2009 14:00:45 I am attempting to break software RAID1 and install the same drives on hardware RAID1 with a new controller card. Reply | Quote

mike |16/01/2010 14:54:07 Nice tut problem is im getting this error "mdadm: fail to stop array /dev/md1: Device or resource busy"" Reply | Quote

thirt |24/01/2010 17:31:01 Mike - Make sure your working directory isn't the filesystem /dev/md1 is mounted on. Also, try using fuser to see what process(s) are in use on the filesystem. i.e: fuser /raid_filesystem Best, Tom Reply | Quote

Jason  - busy |14/12/2011 10:56:12 I too am getting this: "mdadm: fail to stop array /dev/md0: Device or resource busy" When using fuser, it doesn't show anything running. I was able to unmount the array, but I can't get it to stop. So I am stuck at step 4. Ideas? Thanks Reply | Quote

Arun Khan  - RE: Removing RAID Devices |02/06/2010 23:07:36 Great Tutorial. Thanks very much for the clear instructions. With newer kernels I have noticed that it detects the raid devices from the meta data present in the devices itself and hence file /etc/mdadm.conf may not exist. Reply | Quote

nagu  - RAID devices |18/01/2012 01:16:35 Thanku .. for giving good sugession. Reply | Quote

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