best varnishd config for static files

[Kain Sascha]

Hi, 

we run a big picture portal.

We used to cache our files with squid3, but now we want to try varnishd to 
deliver our static files (jpg css and js).

we have 2 varnish servers, caching files from one big static server.
The static server doesnt have the fastest hdds.

The varnishd Servers have 24GB of ram each, and they should use around 20GB of 
them for storing files using LRU, cause the .css and .js should always be 
delivered from RAM.

i compiled and started varnishd like this:

/usr/local/sbin/varnishd -a :80 -b 89.250.xx.xx:80 -s malloc,15360M

I didnt use a config file, because i think i dont need it for static files only.
is this correct?

The Loadbalancing for the two varnish-servers does our software do.

Is this a good solution?

Sometimes im getting a 503 error when the static server has high load.
Also sometimes i am waiting a long time for some files that has to be on RAM 
allready.

best

Sascha