Date: Wed, 21 Feb 2001 17:41:07 -0800 From: Mike Smith <msmith@freebsd.org> To: The Hermit Hacker <scrappy@hub.org> Cc: freebsd-hardware@freebsd.org Subject: Re: IOPs ... what exactly are they? Message-ID: <200102220141.f1M1f8T02912@mass.dis.org> In-Reply-To: Your message of "Wed, 21 Feb 2001 14:56:03 -0400." <Pine.BSF.4.33.0102211440390.16616-100000@mobile.hub.org>
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(this should not have been sent to -smp, redirected)
> Searching google isn't coming up with anything that explains it ... can
> someone point me to some docs, or provide an explanation?
An "IOP" is an I/O operation. IOPs are the MIPS of the I/O world.
> For instance, Tom stated that the 170 does 4000IOPs, vs the 352 at
> 7000IOPs ... yet, the 352 will do twice the sustained transferof the 170
> (200MB/s vs 100MB/s) ... so, IOPs don't == transfer speed ...
That's correct. The IOP rating is a function of the CPU speed and
available I/O; the 352 has twice as many busses as the 170 (hence 200MB/
sec vs. 100), but it's CPU-limited to less than twice on total I/Os per
second.
> And, I imagine (can't get to the Mylex web site right now for some
> reason), the 2000 has an even higher rating then both of those ...
Yes; it has 4 channels and more CPU.
> So, when evaluating what one needs, how do you determine? are there
> thresholds one can work with? 4000IOPs will comfortably handle n xgig
> drives, but if you go above n, then you really need to jump to the 7k IOP
> level else performance drops substantially?
You ignore the IOP rating entirely.
> We're looking at this for a database server, so will most likely be going
> to the 64MB cache level automatically ... but beyond that, I'm virtually
> uneducated :(
Adding cache isn't really useful; it's like a rubber band - unless you
have enough real bandwidth, eventually it'll stretch as far as it can go.
Work out how much I/O your server is going to do, and then scale your
disks accordingly.
--
... every activity meets with opposition, everyone who acts has his
rivals and unfortunately opponents also. But not because people want
to be opponents, rather because the tasks and relationships force
people to take different points of view. [Dr. Fritz Todt]
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