OK, so kind of found this out recently, which is a shame, as it would have saved me having to completely reinstall my system when I added an additional disk to it, to then want to convert it to raid 1 mirroring support.

But nevermind, here is how you can convert your system for additional redundancy against hard disk failure. Of course, hardware raid is better, but for those who don't have the cash - like me, can do it the software way. Incidently, this is more or less the same as the cheap controllers that have software raid in BIOS on the card. So, save some extra cash than buy these equivalents

In this example, I've used partitioning from an 8GB setup I had within vmware. My machines at home are 2 x 160GB, so the principals are the same, just substitute your partitioning where necessary.

Please note, I won't be held responsible for data loss. This is your business, so make sure you have it backed up. This procedure works, I've used it.

Pre-conversion

Here is how my partitions looked like before conversion:



Each partition effectively mounts as follows:



this system was being run as a server, hence the lack of /home, but of course, again, substitute your partitions where appropriate, the procedure is the same. It's important, because when you convert the partitions later, you won't know what they were otherwise.

Install your second hard disk, which in this example becomes /dev/sdb. Once you have both in the system, boot your system normally - no need for recovery disks at this stage. Although I suggest that you run a runlevel 3 while you do this, just do:



or press CTRL-ALT-F1 at the gui to get the console window, login as root and then do:



to stop the X related services.

Altering and creating new partitions

OK, so now we need to convert the partitions. To do this, go into fdisk like this:



We need to toggle each of the partitions, and change them to "fd" which is Linux raid autodetect. To do this, you press the letter "t" and then the number of the partition. In my examples, I have partitions 1, 2, 3, 5 and 6. So:



and so on for each of the other partitions. When finished, press:



and it will save and exit. It will say the new partition table won't be used until reboot, this is perfectly fine and normal because your partitions are mounted, and have to be this way to copy the data off. Now my partitions look like this:



Now we need to make sure /dev/sdb looks the same. You could do this manually with fdisk, but this method is much better:



it will do it all for you, verify with this command:



and make sure the block numbers are the same. They should be. That's your disks configured.

Create arrays and copy data

Since we have /dev/sda in use, we cannot add this to the array yet, and we need to copy the data off before we do, so we create the arrays with /dev/sda missing. This is how:



So, now is the time to create the partitions. In this example, all my partitions were ext3, but find the appropriate command for making your filesystem. Some examples are:



so now, formatting the partitions ready for use (note you use the array devices not the actual /dev/sdx devices):



now, I create a mount point, and start to copy the data across:



you remember, that in my example, /dev/sda3 was my / partition, and when added to the array became /dev/md2. Now to copy the first part:



now mount all other partitions and copy the rest:



Configuration for boot

Now, we need to configure the system so that it will boot. So, edit /etc/fstab and ensure your mount points are correct. Here is mine:



Now, we need to copy this over to the mirrored drive in /mnt/array/etc:



we have to edit /boot/grub/grub.conf (sometimes menu.lst) as well so that it will boot the right place. If you use lilo, then change this as well accordingly and rerun lilo. Here is my grub.conf:



OK, so I used Red Hat for this but the procedure is the same for Mandriva, the text will be different depending on your distro. This also needs copying across:



Now, to finish off the configuration, we need to have a config file for the array, so create /etc/mdadm.conf:



this is enough to ensure it'll boot the system successfully. Now we have to reinstall grub, so:



please note (hd0,1) points to /dev/sda2. /dev/sda1 = (hd0,0) /dev/sda2 = (hd0,2), etc, etc. This is to find your boot config. If you don't have boot separate, then this has to point to the partition that / is on. So if I didn't have /boot, it would be /dev/sda3 in my case if /dev/sda2 was a different partition altogether than /boot.

Finishing off

Now we need to finish off, enter your CD1 and boot from this using:



just exit to the prompt when finished. We now need to delete the stuff on /dev/sda and recreate the partitions, and add to the array. This is simple enough, but first we have to activate the array, so create /etc/mdadm.conf (you did this already, but you're booted from the CD now!):



note that I didn't put /dev/sdax partitions, because they aren't configured correctly yet, they aren't true raid partitions or even added to the array. To activate the array:



this will scan the config file, and all arrays will be active. If it didn't work, it's because the /dev/mdx devices don't exist, so we have to create them if this is the case:



Note, that depending on the array name, the number at the name matches it and rerun the assemble command above. You see the sequence above

Now, you can mount the partitions:



and check in /mnt/array that you can see all the files/directories, etc. This is just to verify you have all the data OK. Now, delete all partitions on /dev/sda with fdisk:



that is enough, partitions 5 and 6 are extended partitions, so by deleting the extended partition 4, they automatically go. Verify it's empty with:



now, we need to create the partitions ready to add them to the array:



and then verify with:



and make sure all is the same. Once OK, let's add the disks to the array that only consists of /dev/sdb partitions so far:



they will add, and now check the status of the array using:



make sure this is completed before continuing, it could take a while if you have large partitions. Now we need to chroot the environment to finish off, I'll explain why in a second:



Because Mandriva (even Red Hat) uses initrd, we have to generate a new initrd. This is simple enough. First off, check your /boot directory for the kernel and initrd. We have to rename the initrd, so here is mine as an example:



normally in Mandriva, there is a symlink called initrd.img which points to initrd-version.img. Here is an example from my Mandriva 2007 machine:



So for Mandriva, you need to move the full initrd-2.6.17-5mdv.img to a backup, here is how I did mine:



substitute filename where appropriate based on your grub.conf file from before. Now, to make the initrd:



the first part is the initrd filename to create, the second is the kernel version you're using. As an example for Mandriva 2007:



would do the trick. After this has been done, you can safely boot the system. If your system doesn't use initrd, then you can skip doing this, as it's not required.

Reboot

Now reboot:



if reboot doesn't work, then type "halt" instead. Some CD's don't have reboot on them, or choose your own appropriate method. Your system should now boot perfectly fine.