RAID

My RAID setup for an Ubuntu NAS box.

Hardware

I used two identical PATA 180GB drives. Each drive was connected to a separate IDE bus (each has their own cable). Do not put two IDE RAID drives on the same IDE bus. Two drives on the same cable would slow everything down plus if one drive goes bad it brings down the entire IDE bus.

software

apt-get install mdadm
apt-get install dmraid

Format

I created a 4GB partition on both drives for the operating system (boot and / on an ext3 partition). The first partition (4G) of each drive was formatted as ext3. I created a second partition on each drives. I left the this partition unformatted. In other words, I installed the full operating system first on the 4GB partition before I even started with RAID configuration. I didn't create a swap partition. I could have, but this machine has 1GB of RAM and will do no work besides SaMBa, so swap isn't going to help much.

After all is said and done I had two drives partitioned and formatted identically:

# fdisk -l

Disk /dev/hda: 180.0 GB, 180045766656 bytes
255 heads, 63 sectors/track, 21889 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/hda1   *           1         486     3903763+  83  Linux
/dev/hda2             487       21889   171919597+  83  Linux

Disk /dev/hdd: 180.0 GB, 180045766656 bytes
255 heads, 63 sectors/track, 21889 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/hdd1               1         486     3903763+  83  Linux
/dev/hdd2             487       21889   171919597+  83  Linux

This setup is not "ideal", but it's easier to setup. I'm building a NAS, so I don't care as much for the integrity of the operating system. I just care about the files in the file server. If the boot sector goes bad I can reinstall Linux and recover my files offline. A more clever system would allow the boot and operating system partitions to be on the RAID array itself.

make the RAID array

I had a small issue where after I created the two partitions (hda2 and hdd2) using fdisk they did not show up in /dev/hda2 or /dev/hdd2. I could see them with 'fdisk -l'. What I did was use cfdisk to create a filesystem on the partitions. After that they showed up in /dev/.

Once the partitions are ready it's easy to turn them into a RAID device:

mdadm /dev/md0 --create --auto=yes --level=1 --raid-devices=2 /dev/hda2 /dev/hdd2

This will create the RAID device /dev/md0 and it will start to "sync" the two partitions. Cat /proc/mdstat to see the status of the resync process:

# cat /proc/mdstat 
Personalities : [raid1] 
md0 : active raid1 hdd2[1] hda2[0]
      171919488 blocks [2/2] [UU]
      [>....................]  resync =  2.5% (4372032/171919488) finish=105.1min speed=26557K/sec
      
unused devices: <none>

Second attempt -- RAID-1 on root

I installed Ubuntu Server as normal on all of one disk. I allowed the installer to repartition and use all of hda. When all was done I had a stock system with the following partition on /dev/hda:

Disk /dev/hda: 180.0 GB, 180045766656 bytes
255 heads, 63 sectors/track, 21889 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/hda1   *           1       21470   172457743+  83  Linux
/dev/hda2           21471       21889     3365617+   5  Extended
/dev/hda5           21471       21889     3365586   82  Linux swap / Solaris

Then I used `dd` to copy the main boot drive to the second drive.

dd bs=1M if=/dev/hda of=/dev/hdd

After that was done I had two identically partitioned drives:

# fdisk -l

Disk /dev/hda: 180.0 GB, 180045766656 bytes
255 heads, 63 sectors/track, 21889 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/hda1   *           1       21470   172457743+  83  Linux
/dev/hda2           21471       21889     3365617+   5  Extended
/dev/hda5           21471       21889     3365586   82  Linux swap / Solaris

Disk /dev/hdd: 180.0 GB, 180045766656 bytes
255 heads, 63 sectors/track, 21889 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/hdd1   *           1       21470   172457743+  83  Linux
/dev/hdd2           21471       21889     3365617+   5  Extended
/dev/hdd5           21471       21889     3365586   82  Linux swap / Solaris