[SQU] squid Pbs when high load, async-io, SMP under linux

Hello,

I have some problems with squid when load become important (60-80 req/s).
Material :

PII-450 Mhz Bi-pro
512 MB RAM
9GB HD SCSI (RAID1 hardware with external controller)
NIC 3com 905b
Debian GNU/Linux 2.2 (with glibc 2.1.3)

Squid :
squid 2.3.4 with squidGuard redirector (15 redirectors started)
Mem config in squid to 128
Cache_dir to 3200 MB
Reiserfs filesystem (r5 hash)

3.6 millions of request per week
40 proxy servers (low load, behind isdn link) that use this one as peer (not all at the same time)

Configure command :

So, when I have high load, squid doesn't respond to request on its port 3128.
If I do a "squid -k reconfigure", it will work for 2-3 minutes and it still hang up...
There is warning and nothing specail in log files.
When I put logging to ALL,2 I see a lot (10 times/s) of "resource temporary unavailable".
But, I don't think it's significative, because the problem still exist even with low charge when squid perform correcty.

I don't increase logging, because log files are very big in a few minutes and there is too much informations to analyse !

So, I have some questions :

1) Is the problem only relative to high load ?

2) Should I disactivate async-io ? Or maybe I can increase the numthreads (16 by defaults, can I put it to 32 or 64 ?)
Is the number of threads have importance with load ?

3) Squid and SMP
I think squid is not (maybe I am wrong ?) using the SMP.
Can I imagine running 2 squid on 2 differents port for reducing the charge for each one ?
I imagine I have to put differents cache_dir and log_dir, so I will lose some caching efficiency, but it doesn't matter in my case :
proxy is mainly used for security and because all clients use a private network addressing...
Do Someone already run 2 squid on the same server ?

4) Do you think I shoud use 2 servers because the load is too important ?
I hope no :)

-------------
Fabien SALVI Centre de Ressources Informatiques
                  Archamps, France -- http://www.cri74.org
                  PingOO GNU/linux distribution : http://www.pingoo.org

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