Software vs Hardware RAID

[feenberg-fCu/yNAGv6M at public.gmane.org (Daniel Feenberg)]

On Fri, 25 May 2007, Rich Braun wrote:

> I did some performance comparisons three or four years ago (posted to this
> list) when I decided to overhaul my hardware RAID1 server.
>
> Rather than buying a new RAID controller, I concluded it was better, cheaper,
> more reliable, faster to go with Linux software RAID.  This is for disk
> mirroring.
>

At one time hardware raid emulated SCSI and could offer OS independence. 
This was a huge benefit, since it let you upgrade the OS without waiting 
for the raid vendor to provide new drivers, and it let you boot from the 
raid array. Nowadays even the best IDE and SATA (3ware) cards require 
drivers, so that advantage is lost. Instead the software raid has the 
advantage since comes with the OS, so it upgrades with the OS 
automatically.

Offloading parity generation hardly seems worthwhile - the cpu is likely
to be waiting for the IO anyway, or have a spare core available.

A warning about Linux RAID 5 - it won't always rebuild. See 
http://www.nber.org/sys-admin/linux-nas-raid.html for my posting on this 
and some other RAID issues.

Daniel Feenberg


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