Re: hot-add unformatted drive to RAID array automagically

[Wouter Verhelst <wouter@debian.org>]

On Thu, Feb 17, 2005 at 11:29:54PM +1100, Russell Coker wrote:
> On Friday 04 February 2005 19:32, Wouter Verhelst <wouter@debian.org> wrote:
> > Having a dedicated processor that does just one task usually implies
> > faster processing than programming a general-purpose processor for the
> > task.
> 
> Not if the dedicated processor has the performance of a 486 and the general 
> purpose processor is a P4 or Athlon.

Sure, but I'd think someone who sells hardware RAID controllers today
with a processor that has the performance of a 486, they need to
seriously look into their business plans.

> > Note, I said "usually". I've seen a number of RAID arrays, and while
> > some are extremely fast, others are even slower than a single regular
> > hard disk when running in RAID5 mode.
> >
> > I've had good experiences with Mylex RAID-controllers in that regard.
> 
> In late 2000 I did some benchmarking of a Mylex Dac960 controller.  It gave a 
> maximum performance for bulk linear reads/writes of about 10MB/s.  Linux 
> software RAID gave 30MB/s on the same test with slower disks.  However the 
> Mylex gave good performance for random seeks, extra caching I guess.

I haven't done any benchmarks, and no longer have access to the hardware
I was talking about (previous job). Back then, I regularly had to set up
RAID-based systems where the increased availability of the system was
far more important than the speed (systems were being used for a
telnet-based application); so the actual RAID controller being used
would depend on which one was in promotion at that time. It would either
be a Mylex or an Adaptec one; occasionally something entirely different.
The Mylex controllers were by far the fastest ones.

Theoretically, having a dedicated processer also means the main
processor is free to do other things (as long as it doesn't require disk
access). If the controller is up to snuff, it should thus be faster.

I didn't say that a hardware RAID5 setup is /always/ faster than a
software one; everything depends on the RAID controller in question.
However, in theory, if the controller is a modern and good quality one,
it should be.

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