EC2 raid10 for mongo db

Running mongo db on a raid10(software raid) into ec2 is done via the ebs volumes. I'll show you how to

• create the raid10 on 8 ebs volumes
• (re) start the mdadm on the raid device
• mount the raid10 device and start using

I didn't use any config files for the raid devices so you will need to know how the devices are mapped and what uuid has the raid10.

Initial Creation of the raid

# you will need to have your ebs volumes attached to the server
mdadm --create --verbose /dev/md0 --level=10 --raid-devices=8 /dev/sdj /dev/sdk /dev/sdl /dev/sdm /dev/sdn /dev/sdo /dev/sdp /dev/sdq

# now create a file system 
mkfs.xfs /dev/md0

#mount the drive
mount /dev/md0 /mnt/mongo/data


# Obtain information about the array
mdadm --detail /dev/md0 # query detail

/dev/md0:
        Version : 0.90
  Creation Time : Wed Oct 26 19:37:16 2011
     Raid Level : raid10
     Array Size : 104857344 (100.00 GiB 107.37 GB)
  Used Dev Size : 26214336 (25.00 GiB 26.84 GB)
   Raid Devices : 8
  Total Devices : 8
Preferred Minor : 0
    Persistence : Superblock is persistent

    Update Time : Mon Dec 12 15:56:48 2011
          State : clean
 Active Devices : 8
Working Devices : 8
 Failed Devices : 0
  Spare Devices : 0

         Layout : near=2
     Chunk Size : 64K

           UUID : 144894cd:3b083374:1fa88d23:e4200572
         Events : 0.30

    Number   Major   Minor   RaidDevice State
       0       8      144        0      active sync   /dev/sdj
       1       8      160        1      active sync   /dev/sdk
       2       8      176        2      active sync   /dev/sdl
       3       8      192        3      active sync   /dev/sdm
       4       8      208        4      active sync   /dev/sdn
       5       8      224        5      active sync   /dev/sdo
       6       8      240        6      active sync   /dev/sdp
       7      65        0        7      active sync   /dev/sdq

# note the UUID and the devices
# Start the mongo database
/etc/init.d/mongod start

Shutdown(reboot) the server 

# restart the array device - you need to have the ebs volumes re-attached!
mdadm -Av /dev/md0 --uuid=144894cd:3b083374:1fa88d23:e4200572  /dev/sd*
mdadm: looking for devices for /dev/md0
mdadm: cannot open device /dev/sda1: Device or resource busy
mdadm: /dev/sda1 has wrong uuid.
mdadm: cannot open device /dev/sdb: Device or resource busy
mdadm: /dev/sdb has wrong uuid.
mdadm: cannot open device /dev/sdc: Device or resource busy
mdadm: /dev/sdc has wrong uuid.
mdadm: cannot open device /dev/sdr: Device or resource busy
mdadm: /dev/sdr has wrong uuid.
mdadm: cannot open device /dev/sds: Device or resource busy
mdadm: /dev/sds has wrong uuid.
mdadm: /dev/sdj is identified as a member of /dev/md0, slot 0.
mdadm: /dev/sdk is identified as a member of /dev/md0, slot 1.
mdadm: /dev/sdl is identified as a member of /dev/md0, slot 2.
mdadm: /dev/sdm is identified as a member of /dev/md0, slot 3.
mdadm: /dev/sdn is identified as a member of /dev/md0, slot 4.
mdadm: /dev/sdo is identified as a member of /dev/md0, slot 5.
mdadm: /dev/sdp is identified as a member of /dev/md0, slot 6.
mdadm: /dev/sdq is identified as a member of /dev/md0, slot 7.
mdadm: added /dev/sdk to /dev/md0 as 1
mdadm: added /dev/sdl to /dev/md0 as 2
mdadm: added /dev/sdm to /dev/md0 as 3
mdadm: added /dev/sdn to /dev/md0 as 4
mdadm: added /dev/sdo to /dev/md0 as 5
mdadm: added /dev/sdp to /dev/md0 as 6
mdadm: added /dev/sdq to /dev/md0 as 7
mdadm: added /dev/sdj to /dev/md0 as 0
mdadm: /dev/md0 has been started with 8 drives.

# now you can mount the array
mount /dev/md0 /mnt/mongo/data/

# start the mongo database
/etc/init.d/mongod start