Large, busy, caches... problems?

I'm still struggling to get one of the HENSA Cache boxes to run Squid
(1.1.8) in an efficient manner.

The cache_swap setting has recently been reduced to 2000(MB) to see if
this would improve performance. Previous settings of 4500(MB) and
16000(MB) have caused the cache to be unusable, with delays of >30
seconds in retrieving local documents.

With the 16GB cache (which never managed to grow beyond 8GB) it became
obvious that there was insufficient memory to store the object meta
data in memory. I had hoped that a reduction to 4.5GB might help.
The reduction to 2GB has not helped completely either.

The system seems to perform well until it starts cleaning. Once
cleaning starts the system appears to begin paging, becoming worse
over time (although this does not appear to be the only factor causing
delays, the system is currently slow but does not appear to be paging
[just my luck!]). Observations of the information reported by the
cache manager interface suggest that the maximum resident size
stabilises at around 80MB.

I would like to increase the cache size (2GB does not give us a
particularly high hit rate compared to our other machines) - ideally
to 4.5GB (or higher - the machine has 16GB available!). I have been
told that if I can show that the problems will be 'resolved' by adding
memory then it may be possible to purchase an additional 128MB RAM.

Would other users of large, busy, caches care to comment on their
experiences? (Particularly with respect to the problems encountered
when paging or operating during the clean cycle.)

In an attempt to reduce memory overheads, all FTP requests are farmed
out to another of our machines.

cache_mem = 4
cache_swap = 2000

The disk cache is distributed over 8 XFS disk partitions (each
partition on a separate physical disk)

The machine in an SGI Challenge S, IP22, running IRIX 5.3 and is
dedicated to running the cache.

I have tried 1.NOVM.8 but this crashes too frequently for use. It
appears that the system runs out of file descriptors (2500 reported
available upon startup).

(My apologies for continued pleas for help - I want to get this thing
working so that we can do some work with ICP with our other machines
and child caches within the UK.)

Ian

-- 
HENSA Cache Administrator  Tel: +44 (0)1227 823769
                           Fax: +44 (0)1227 762811