RAID instalando Centos 5.2

The easiest way to setup a software RAID filesystem is to create it at install time, when you install your RHEL with the CDs. When you come to the partitionning section of the installation at the beginning, you will be able to choose 'Disk Druid' to partition your disks. Choose this one and follow these steps:

1. Create your partitions as you normally do on the first disk. However, use the 'Software RAID' filesystem type instead of ext3. It's at the RAID level that you will specify the ext3 filesystem later. For the /boot partition, put it first and choose 'set as primary', because else disk druid will change it's order.

2. Once /boot, / and a swap partition (minimum) have been created, you must copy this partition information on the second drive, because the two disks must be identical. To do that, click on the 'RAID' button and choose 'clone drive'. Else you can just do exactly the same things that you did on the first drive to the second drive, it works fine also. I suggest you put 100Mb for /boot, and twice the RAM memory you have for the swap partition.

3. Create the software raid partitions, by clicking on 'RAID' and then 'create a RAID device like /dev/md0'. Once there, you have to choose which partitions to include to the mount point that you will specify. Here is the recommended method: - /boot = /dev/md0 (always 100Mb) - swap = /dev/md1 (between 1 to 4 Gb) - / = /dev/md2 (rest of the disk)

Also, choose the 'ext3' filesystem instead of 'ext2', which is much more reliable even if a little bit slower. Put the swap partition just after the boot partition, because then you should theoretically win some speed performance because it will be a short way between the swap and the RHEL root files installation (if you have hundreds of Gb on the root partition and you put the swap partition after that, then you might loose each time the whole length of the disk to seek the datas and this might be much longer..). Choose the RAID level you wish for each partition. RAID 0 is striped (doubles volume but no redundancy). RAID 1 is mirroring. It has redudancy and accelerates the read time. This is a very good level. RAID 5 needs at least 3 disks. Also, choose the RAID members for this RAID partition. You should put the correspondig partition for each disk hda and hdb only. This means that you will check only two partitions, one for each drive.

Once this is done, you can continue with the installation process. At the end, you will still have to make your second disk be bootable and save the partitions (see further on).

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As for how to make both boot partitions boot so that if one of both disks fails the system would still boot up, this is my note about it, but works only for CentOS 3. On CentOS 4 I have no idea:

raidstop /dev/md0 fdisk /dev/hda type 't' and then '1' for boot partition, and then 'fd' for the Linux raid autodetect filesystem, and finally 'w' to save changes to the disk and quit. Do the same with the second disk of the array.

Hope this helps.