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Re: severe I/O performance issues on 2.4.22 SMP system

On Sat, Nov 01, 2003 at 08:26:40AM +1100, Glenn Hocking wrote:
> Hi Daniel
> My experience is that SMP is only great in some specific situations,
> normally where all the software and hardware is built for the specific
> SMP implementation.
> As an example, I had a lot of problems with DPTs RAID controllers when
> they moved to I20 based hardware, and I started using Dual Xeon
> processor systems. 
> DPT investigated quickly and found that the lock timers that counted
> to ever increasing numbers while waiting for IO, keep hitting their
> maximum digit size in software as the server was just too fast.

I'll definitely keep this in mind, as I have several servers using DPT
controllers. :)  The whole thing is pretty maddening, as I was
previously using the same model of QLogic card and the same kernel
version on a dual PIII 1Ghz system without these problems (but with
plenty of other problems caused by flaky hardware).

> I'm not sure about your specific situation, but the symptoms that you
> state are identical to these issues that I had. I tend these days to
> not use SMP much as most SMP systems tend to be Hybrids, with
> anomalies that just waste too much time trying to solve. I tend to
> just run more servers for the same application, which does also
> provide some form of redundancy. If I run two fast mail servers rather
> than one huge SMP system, I only loose half my email when a component
> or upgrade fails. This also tends to be a cheaper, easier to get going
> and maintain.

This is the direction that I'm planning to move, but it will probably
require an expensive NetApp storage server, as splitting the email
storage among multiple servers isn't an option for me (without extensive
software modifications to make the whole thing transparent to clients).

> Hope this helps.

It does -- thanks again for the reply!


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