[K12OSN] Linux "Software RAID"
Rob Owens
rowens at ptd.net
Fri Aug 8 00:13:05 UTC 2008
On Thu, Aug 07, 2008 at 03:20:21PM -0400, Terrell Prude' Jr. wrote:
> Carl Keil wrote:
> >Hey Folks,
> >
> >I hear people extolling the virtues of "software RAID" on the list a
> >lot. I'm finally setting up a production server in a school and I
> >have enough disks to play with to do RAID. I'm leaning towards RAID
> >5. Anyway, when people say "software RAID" do they mean just setting
> >up a RAID in LVM Manager? Or is the mdadm command the simpler, more
> >robust, preferred way to do this? I never thought about using LVM for
> >this before, but the last time I was in there I noticed some RAID
> >options. This is for a Samba/LDAP/home directory server.
> >
> >Thanks,
> >
> >ck
>
> "Software RAID" is simply doing the RAID (striping, mirroring, parity,
> whatever) in the OS instead of on a dedicated card. Windows NT, from at
> least v3.50 (way back when), can do this, and Linux can do it as well.
>
> If you're thinking of RAID 5, which is my preferred level, I'd avoid
> doing it in software and instead opt for a dedicated RAID card.
> Something like an LSI MegaRAID 150-6 SATA controller. If you do it in
> software, you'll eat up some CPU doing the parity calculations, so you
> definitely want to offload that. However, for just mirroring (say, RAID
> 1), you should be fine, because the CPU hit for mirroring is minimal.
>
I hear lots of people talk about the CPU hit of software RAID. But how much hit is there really? Suppose for argument's sake I can get a hardware RAID card for $100. If I instead used software RAID and spent my $100 on a better CPU, wouldn't I be ahead of the game?
-Rob
More information about the K12OSN
mailing list