raid drive setup

Ronayn · 05-25-2012, 10:32 AM

Apologies in advance, as I am complete novice on this topic and not sure how to phrase the question.

I have an HP server with several physical hard drives. When the server is powered on, it goes through a raid controller check that allows the option of setting up logical drives (in various configurations).

My question is, if I configure a logical drive as a raid of a few physical disks, do I have to configure them the same way in the OS? Or is a the server level raid completely seperate from an OS level raid?

I am not sure if I am explaining this very well, so I going to give more detail:

The HP server is blank, so normally I go through the raid controller to setup the logical drives. Once that is done, I set the server for PXE boot which pulls my kickstart file that contains the following lines:

Code:

clearpart --all --initlabel
part /boot    --fstype ext3   --size=100                             --ondisk=cciss/c0d0   --asprimary
part swap                     --size=1000   --grow  --maxsize=2000   --ondisk=cciss/c0d0
part /        --fstype ext3   --size=1      --grow                   --ondisk=cciss/c0d0
part /data1   --fstype ext3   --size=1      --grow                   --ondisk=cciss/c0d1

My question is should I be setting these up as a raid in the kickstart file -- or, again, is the server's raid different from an OS raid (if so, I am assuming you only use one of the other -- if not, I am guessing that you have to have them match).

Ser Olmy · 05-25-2012, 10:45 AM

The RAID controller presents one or more logical drives to the host OS through the controller driver. The number of logical drives depend on how you've configured your drives, but typically does NOT match the number of actual, physical drives.

If you have four SATA drives configured as a RAID 5 volume, that volume will appear as a single, physical drive in Linux (for instance, /dev/sda). You partition and use /dev/sda as were it a regular disk, and use software from the controller manufacturer to monitor the status of the RAID array and the physical drives in it.

Exception: If the controller is a low-end so-called "fakeRAID" controller (like those used in the ProLiant ML and DL 1xx series), the physical drives may actually be visible as /dev/sda, /dev/sdb etc. You still do not need to configure the RAID setup twice, but you typically use a slightly different kind of driver which attaches to the physical devices and produce the logical RAID device(s). dmraid is one such driver.

Edit: I see you're using the older cciss block device driver. Nothing wrong with that, but your RAID volumes will appear as /dev/cciss/cxdy, with x being the controller number and y the logical RAID volume number.