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Re: RAID

Richard Stevenson wrote:
> 
> On 2 Mar 2000, at 16:36, Steve Tickle wrote:
> 
> > It occurred to me that as the amount of data we want to back up could
> > increase dramatically we could consider RAID.
> > My question is, what software RAID systems exist for linux, what's
> > involved
> > and how much of a pain are they to set up?
> 
> RAID support is in the kernel source - you need to either compile a kernel
> with support, or check to see if the module (md.o, IIRC) exists on your
> system.  You can't boot from an md device unless you're *really* keen on
> hacking low-level stuff, but you could put all of your data partitions on a
> RAIDset.  I haven't actually worked with it, though... I've only ever had
> hardware RAID to deal with.  Doing RAID-5 in software means a performance
> hit... lots of parity calculations going on.

You _can_ boot when your / filesystem is on a software-raid.
You can certainly boot from hardware raid (the raid device gets shown
as /dev/sda (or something)).

read:
/usr/doc/HOWTO/Root-RAID-HOWTO
/usr/doc/HOWTO/mini/DPT-Hardware-RAID
/usr/doc/HOWTO/mini/Software-RAID
/usr/doc/raidtools-0.90/Software-RAID.HOWTO.txt

or do a man -k raid to see some manualpages

Contrary to popular beliefs, software raid is in may cases faster
than hardware raid, especially with older raid controllers and a
fast cpu.

> You might also want to look at journalling filesystems - ext3 is probably a
> bit raw at the moment, but ReiserFS is supposed to be coming along quite
> nicely.  They were hoping to get it into the 2.4 kernel, but I don't think
> that's going to happen.

One of the reasons for choosing RAID is to be failsafe. This doesn't
go hand in hand with using a beta-filesystem :-)
On the other hand, it's a pain to see your production system take
hours to fsck a 40GB raid array.. 

Jules
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