Re: [squid-users] Squid Scalability

Gavin McCullagh wrote:
> Hi,
>
> On Tue, 07 Apr 2009, Amos Jeffries wrote:
>
>> Gavin McCullagh wrote:
>
>>> Mine too. The operating system is on linux software RAID1 partitions so I
>> Ah, there we probably have the answer as to why there is so much iowait.
>
> I'm not convinced of that. The iowait seems to grow directly as a function
> of the cache size and the caches themselves are not RAIDed. You can see
> that I recently reduced the cache size and got an immediate, substantial
> reduction in iowait.
>
> http://deathcab.gcd.ie/munin/gcd.ie/watcher.gcd.ie.html#Squid
> http://deathcab.gcd.ie/munin/gcd.ie/watcher.gcd.ie.html#System
>
>> You may want to find out how to determin RAID iowait vs other iowait and
>> see what shows up.
>
> That would be interesting alright. I'll see what I can find out.
>
>> Though I only had 2x 250GB disks on 2.6GHz box RAID1, Squid maxed out
>> and started seriously lagging requests under 3 users (at around ~5Mbps
>> wild guess).
>
> Did you have the cache on RAID1 or the OS or both? Hardware or software
> RAID (not that my using software should improve anything of course)?
>
>> I shifted to a *slower* 1.8GHz box with single OS-shared disk and it now
>> hits serves 15 users without sweating and runs dozens of reverse-proxy
>> domains as a side job.
>
> Squid's usage of CPU time doesn't seem to be an issue for us at all so I
> can well believe that.
>
>> My review of RAID + Squid was overruled by some RAID experts with more
>> experience. I'm still puzzled how they got the evidence for
>> "performance: quite good" on software RAID though, maybe dual-core
>> minimum, mine are both singles.
>
> I can certainly see how putting the cache on software RAID1 is a bad plan,
> but that's not what I've done and the iowait is sensitive to cache size.
> I have the squid logs and the squid cache on single disk partitions. I
> don't think the OS shouldn't be loading the disk too much.
>
> Many thanks for your help on this,
>
> Gavin
>

ah, got me wires crossed. sorry there.

Amos

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