How-to Start and Stop Linux Software RAID Devices

If you have followed along in our Linux RAID How-to, your RAID array should start and stop automatically as your system boots and shuts down.  However, should you want to reconfigure the array or remove it all together, you will need to know how to start and stop the array manually.  In this KB we will show how to start and stop the array, you can refer to the Linux RAID How-to for configuration references and links to other RAID KB articles.  Let's get started!

Starting the RAID Array

1. Use mdadm to start the RAID device
   
   

   [root@Linux01 /]# mdadm --assemble --scan mdadm: /dev/md0 has been started with 3 drives. [root@Linux01 /]#

For those who have not added the array configuration information to the /etc/mdadm.conf file there is still hope yet.  Starting the array without a /etc/mdadm.conf file is a two step process.  You must first find the UUID of the array you wish to start, and then start the array with the UUID qualifier.

1. Assuming we know one of the devices that make up the array, we can examine the device and extract the UUID with the mdadm tool
   
   

   [root@Linux01 ~]# mdadm --query /dev/sdb1 /dev/sdb1: Magic : a92b4efc Version : 00.90.00 UUID : 25ab199d:9cf31f9d:5fefdf2f:865b1a2e Creation Time : Tue Jun 16 13:24:49 2009 Raid Level : raid5 Used Dev Size : 4192832 (4.00 GiB 4.29 GB) Array Size : 8385664 (8.00 GiB 8.59 GB) Raid Devices : 3 Total Devices : 3 Preferred Minor : 0 : Update Time : Tue Jun 16 13:32:17 2009 State : clean Active Devices : 3 Working Devices : 3 Failed Devices : 0 Spare Devices : 0 Checksum : e6c5297b - correct Events : 0.2 : Layout : left-symmetric Chunk Size : 64K : Number Major Minor RaidDevice State this 0 8 17 0 active sync   /dev/sdb1 . 0 0 8 17 0 active sync   /dev/sdb1 1 1 8 33 1 active sync   /dev/sdc1 2 2 8 49 2 active sync   /dev/sdd1

   
   
2. Use the UUID from step #1 to start the array
   
   

   [root@Linux01 /]# mdadm /dev/md0 --assemble -u 25ab199d:9cf31f9d:5fefdf2f:865b1a2e mdadm: /dev/md0 has been started with 3 drives. [root@Linux01 /]#

   
   
3. Add the array configuration information to /etc/mdadm.conf so you do not have to reference this KB again ;-)
   
   

   [root@Linux01 /]# mdadm --detail --scan >> /etc/mdadm.conf [root@Linux01 /]#

Stopping the RAID array

Stopping the RAID array is fairly straight forward, unmount the array and then issue the mdadm stop command.

1. Check to see if the RAID device is mounted
   
   

   [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
   
   
2. Unmount the RAID device
   
   

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

   
   
3. Stop the RAID device
   
   

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

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Ashwin |15/02/2011 11:20:13 Excellent tutorial. Good job. Reply | Quote

Anonymous |31/03/2011 04:10:36 which is the command for start raid Reply | Quote

Alpha01  - Ruby Ninja |26/04/2011 12:22:14 This article totally saved my behind. Thanks! -Tony Reply | Quote

Martin Klier  - How to identify the UUID |27/06/2011 07:25:16 If you are looking for a md-device's UUID (for example for the fstab), just ll /dev/disk/by-uuid on newer linuxes. Regards Martin Reply | Quote

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