Software raid + separate partitions?

Question

I have setup software RAID1-arrays using two 250GB harddrives. There's two arrays - one named md0 in which the system is kept and the other, md1 works as swap:

# cat /proc/mdstat 
md0 : active raid1 sda1[1] sdb1[0]
      239256512 blocks [2/2] [UU]

md1 : active raid1 sda2[1] sdb2[0]
      4940736 blocks [2/2] [UU]

To keep things a bit more organized, I would like to use separate partitions for /tmp, /home, /var, /opt & and so on in the future. Do I need to create separate arrays for each partition or can I someway let my current md0 contain all these partitions without creating a dozen additional arrays?

Thanks

Answer 1

Mat already said it. I will give you a quick example of a standard layout for software raid and LVM:

• sd[ab]1: /boot, 256MB - can be run as Raid1 (md0), install grub on both partitions
• sd[ab]2: /, 3GB - run as Raid1 (md1)
• sd[ab]3: md2 - use for VG system:

After you created md2:

1. pvcreate /dev/md2
2. vgcreate system /dev/md2
3. lvcreate -n vartmp -L 2G system
4. mkfs -t ext3 -L vartemp /dev/system/vartemp
5. mount /dev/system/vartemp /var/tmp

I hope that is enough to get the idea. You can use LVs just like you would use a partition. If / is big enough, you can start by installing everything there, then set up your LVs and move the contents there after you booted from a rescue ISO/DVD/CD.

Answer 2

Older versions of the mdadm utility and Linux kernel (2.4) did not support partitioning of software RAIDs. This was introduced in the 2.6 kernel, but partitioning of so-call "non-partitioned" arrays was not introduced until 2.6.28.

From mdadm man page:

The standard names for non-partitioned arrays (the only sort of md array available in 2.4 and earlier) are of the form

          /dev/mdNN

   where NN is a number.  The standard names for partitionable arrays
   (as available from 2.6 onwards) are of the form

          /dev/md_dNN

   Partition numbers should be indicated by added "pMM" to these,
   thus "/dev/md/d1p2".

   From kernel version, 2.6.28 the "non-partitioned array" can actually
   be partitioned.  So the "md_dNN" names are  no longer needed, and
   partitions such as "/dev/mdNNpXX" are possible.

If you're using a version of mdadm older than 3.0, mdadm is responsible to create all the device nodes (see the --auto option). Later versions rely on udev.