Running RAID in a Fedora System

[Warren Togami]

Allan Metts wrote:
> Hi all,
> 
> I'm setting up Fedora in a server with five identical SCSI disks and a 
> hardware RAID controller.  I want reliability AND performance, so I 
> understand my options here are either RAID5 or RAID 0/1 (combination of 
> striping and mirroring).
> 
> Any advice on how I should set this box up?  I know RAID 5 would give me 
> the equivalent of 4 disks and full recoverability -- but how do I go 
> about performing such a recovery operation after a disk failure in 
> Fedora?  Or does the Adaptec controller handle this automagically 
> somehow?  My ignorance here has me leaning towards striping/mirroring -- 
> simply because I think I understand how recovery works.
> 
> If this was your server, how would you set up the five disks?

True hardware RAID controllers handle fail-over and automatic rebuilding 
automatically, although you probably want to install tools that allow 
monitoring and reporting of the hardware status.  I am not too familiar 
with those tools so you need to search documentation.

RAID 0+1 with four disks and one hot-spare would be the absolute fastest 
option.  RAID 0+1 gives you the both striping and mirroring, meaning 
theoretically higher throughput and redundancy at the expense of disk 
space.  Your storage capacity is then equivalent to two disks.

RAID 5 does striping across all disks in a staggered fashion, using XOR 
(?) on one extra disk for checksum.  This means that if any one disk 
fails, the controller can read information from the other disks and 
rebuild the hot-spare.  RAID 5 theoretically has higher read speed 
because of its striped nature, but writing performance is diminished. 
Your storage capacity is equal to the number of disks in RAID 5 array 
minus one, which is a bit more efficient than RAID 0+1 in space usage.

I personally like maximum performance so I would go with RAID 0+1 plus 
hot-spare, but it really is your choice.

Warren