On Tue, 30 Sep 2008 19:26:36 PDT Anon Y Mous <system5unix at yahoo.com> wrote:
> I think it's even possible to prove mathematically that those
> hardware RAID cards will run slower than software RAID if you have a
> good CPU like an AMD Opteron or an Intel DuoCore with 2 gigs of RAM.
I don't like hardware raid for political reasons: hardware raid means
my data, on my disks, can't be accessed without the cooperation of
that hardware raid vendor. If there were a standard for hardware raid
such that I could move the drives to cards from three or more vendors,
that would be acceptable. But as things are, once I've got stuff in a
hardware raid, I have to use that vendors raid hardware.
As for performance, you will always eventually be able to buy a CPU
that will run RAID work faster than any given piece of hardware will
do it. The key word is "eventually" - you may have to wait for the CPU
vendors to catch up. However, CPUs are getting faster faster than such
special-purpose hardware, so the wait is in general getting shorter.
But doing the RAID work faster doesn't mean you've made the system
faster, just the disk. The total work the system can do with software
raid is the same as the total work the CPU can do. With hardware raid,
the total work the system can do is the work the CPU can do PLUS the
RAID work, which the CPU is no longer doing. So shifting to software
RAID can make your disk subsystem faster while at the same time
lowering the total system throughput, depending on the workload.
<mike
--
Mike Meyer <mwm at mired.org> http://www.mired.org/consulting.html
Independent Network/Unix/Perforce consultant, email for more information.
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