RAID Cards

[Dan Nelson]

In the last episode (Jun 30), Mark Bucciarelli said:
> On Thu, Jun 30, 2005 at 04:48:18PM -0400, Simon wrote:
> > Just because there is no monitoring tool available due to lack of
> > support, doesn't mean the card itself is bad. I much prefer
> > hardware implementation than software.  True hardware RAID frees up
> > a lot of CPU time if you have heavy IO and software just can't keep
> > up if you utilize CPU intensive apps.
> 
> Why do you say hardware raid frees up "a lot of CPU time?"  Have you
> measured this?
> 
> Do you have any servers that are cpu-bound instead of io-bound?
> 
> I am having this exact discussion with my business partner at the
> moment--he is also a proponent of hardware raid.  I don't see the big
> win in hardware raid.

The three big plusses for hardware raid are: if you get one with
battery-backed cache (strongly recommended), then the array can cache
raid-5 writes until it gets full stripes, and can hold off doing mirror
writes if there are pending read requests.  Also, if your power goes
out or the system spontaneously reboots, you won't have to rebuild
parity or resync the mirrors (assuming battery-backed cache).  And
finally, hardware raid cards will automatically rebuild onto a hot
spare if available and you can swap out the dead drive and swap a new
spare in without having to run a single command.

-- 
	Dan Nelson
	dnelson at allantgroup.com