Oct 082014

Another reminder to myself, so I don’t forget it again.

Warning: Use this on your own risk! You might lose all the data stored on any of the hard disk drives if you make a mistake!

To create a new raid, all the disks must be partitioned first.

To actually create the RAID we need the tool mdadm which is not installed (on Ubuntu Server) by default.

apt-get install mdadm

This will also install a few dependencies, in particular it will install a mail transfer agent (MTA, postfix in my case). This MTA needs to be configured so it can send e-mails to the administrator (root).

Creating the raid is as easy as typing:

mdadm --create /dev/md0 --level=5 --raid-devices=4 /dev/sdb1 /dev/sdc1 /dev/sdd1 /dev/sde1

Mdadm might detect that the disks have already been used in a different raid and will warn you. It then gives you the option to continue creating a new array or not.

Create an ext3 file system on the newly created RAID device with the label “daten1”:

mkfs --type=ext3 -L daten1 /dev/md0

This takes quite a while.

To automatically start the RAID, it must be added to mdadm.conf:

mdadm -Es | grep md[0-9]  >>/etc/mdadm/mdadm.conf

Note that this will append to mdadm.conf, so if you execute it multiple times you will get duplicate entries. So make sure to check the file afterwards.

To mount the partition, it must be added to /etc/fstab like this:

/dev/md0    /mnt/daten1   ext3    defaults,noauto

noauto means that it should not be mounted automatically on boot. This is a safeguard against boot failures on headless servers. If any of the automatically mounted devices fails. We don’t reboot our servers very often so we will just ssh into it after reboot and mount the partition manually with

mount /mnt/daten1

To check the RAID status, use

cat /proc/mdstat

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