[CentOS] Manual Paritioning with fdisk

Tue Apr 12 04:19:52 UTC 2005
dan1 <dan1 at edenpics.com>

Hello, Gerald.

This is my personnal step by step documentation about how to install 
software RAID with CentOS 3 or 4.


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 
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).


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.


----- Original Message ----- 
From: Gerald Waugh
To: CentOS mailing list
Sent: Tuesday, April 12, 2005 12:34 AM
Subject: Re: [CentOS] Manual Paritioning with fdisk

On Mon, 2005-04-11 at 17:20 -0500, Les Mikesell wrote:

> Won't such a machine crash when one of the drives containing swapped-out
> data dies?

swap must be mirrored.

For the life of me I can't get disk druid to create RAID partitions

Could someone give me a step-by-step ;) Please!


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