Setting up Soft RAID

This is a very quick guide to setting up a Linux software RAID.

All these examples are same for RAID0 and RAID1

0. Disclaimer
Make sure you back up all your data, or you have empty hdds before you proceed.

1. Disk management
I’m using 2 same HDDs with 400Gigs.

1 2	Disk /dev/sdb: 400.0 GB, 400088457216 bytes Disk /dev/sdc: 400.0 GB, 400088457216 bytes

I created on both disks new partitions with parted (also you can use gparted):

1 2	/dev/sdb1 1 48641 390708801 83 Linux /dev/sdc1 1 48641 390708801 83 Linux

2. Raid creation

1 2	$ aptitude update $ aptitude install mdadm

For RAID-0

1	$ mdadm --create /dev/md0 --level=0 --raid-devices=2 /dev/sdb1 /dev/sdc1

For RAID-1

1	$ mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sdb1 /dev/sdc1

3. Get RAID information

1 2	$ fdisk -l Disk /dev/md0: 800.1 GB, 800171491328 bytes

$ cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] 
md0 : active raid0 sdc1[1] sdb1[0]
      781417472 blocks 64k chunks
 
unused devices: <none>
</none>

1 2	$ mdadm --detail --scan ARRAY /dev/md0 level=raid0 num-devices=2 metadata=00.90 UUID=fb3d1fd3:5dd2b871:01f9e43d:ac30fbff

$ mdadm --detail /dev/md0 
/dev/md0:
        Version : 00.90
  Creation Time : Fri Aug 27 21:27:51 2010
     Raid Level : raid0
     Array Size : 781417472 (745.22 GiB 800.17 GB)
   Raid Devices : 2
  Total Devices : 2
Preferred Minor : 0
    Persistence : Superblock is persistent
 
    Update Time : Fri Aug 27 22:46:13 2010
          State : active
 Active Devices : 2
Working Devices : 2
 Failed Devices : 0
  Spare Devices : 0
 
     Chunk Size : 64K
 
           UUID : fb3d1fd3:5dd2b871:2ce552e4:6d63ea58
         Events : 0.3
 
    Number   Major   Minor   RaidDevice State
       0       8       17        0      active sync   /dev/sdb1
       1       8       33        1      active sync   /dev/sdc1

4. Create file system
That all you have a running RAID array, to use it you need to create a filesystem for example ext3 one.

1	mkfs.ext3 /dev/md0

Delete RAID array:

1	mdadm --stop /dev/md0

To make sure it doesn’t come back, you need to delete the RAID super blocks…

1 2	mdadm --misc --zero-superblock /dev/sdb1 mdadm --misc --zero-superblock /dev/sdc1

You can mount your raid partition automatically on server start:

1	vim /etc/fstab

And add this line to it:

1	/dev/md0 /mnt ext3 defaults 0 0

md0 will automatically mounted to /mnt/

Start a partially built array:

$ mdadm --run /dev/md0
 
 
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] 
md0 : active raid1 sdb1[0] sdc1[1]
      390708736 blocks [2/2] [UU]
      [&gt;....................]  resync =  0.0% (277568/390708736) finish=70.3min speed=92522K/sec

Don’t forget the RAM usage:

Setting up Soft RAID

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