[LUNI] simple RAID question

[Ramin K]

luther rochester wrote:
> I'm setting up a new Dell Poweredge 2950 server for work. I've never 
> done RAID before, and I'm a bit confused.
> 
> The machine has 8 x 73GB drives on a PERC 5/I RAID controller.
> 
> I was under the impression I could set this up in RAID 1 so I would end 
> up with 4 mirrored 73GB drives. However, when I set it up for RAID 1 and 
> installed, now my OS doesn't recognize any drives other than the single 
> 73GB.
> 
> Was I wrong in assuming I could configure it multiple ways (the only 
> options on setup were whether I wanted RAID 1,3,5, or 10)? Does 1 
> controller = one drive?
> 
> Please help a RAID noob out.

What sort of setup are you looking for, RAID 10 or just fours sets of 
RAID 1 pairs?

The thing to remember is that the card does not really talk to the OS 
that much. So if you have configured four RAID sets it's going to appear 
to the OS as /dev/sda, /dev/sdb, /dev/sdc, etc. Chances are your 
installer is only going to catch the first one and you'll have to 
manually edit /etc/fstab to add the rest. Running dmesg should show you 
that the OS did query the RAID card and should see the devices. If it 
didn't I'd go back into the RAID config and make sure the devices are there.
	You will also need to do the whole build, initialize, etc steps for 
each RAID you create or they won't appear either.
	If you're just building this and your files sizes tend to be large, a 
couple of MB and up as opposed to mail which averages 12k, you might 
want to raise the cluster size from 32-64k to the 128-256k range. I'm 
not sure what the defaults are on the 2950.

	If you're looking for RAID 10, RAID 0 striping of RAID 1 pairs which is 
popular for databases, you will need to do that within the RAID card. 
The config is a bit weird IIRC and you might need to track down the info 
on Dell's site. The good news is that the 2950 supports a real RAID 10 
rather than RAID 10 concatenated or whatever they called it on the 2850.

Ramin