[squid-users] Overflowing filesystems

I am running this version of squid:

Squid Cache: Version 2.5.STABLE10
configure options: --enable-large-cache-files --disable-internal-dns
--prefix=/opt/squid --enable-async-io --with-pthreads --with-aio
--enable-icmp --enable-snmp

specifically enabled for large files. My cache_dir is 535GB and the
cache_dir directive looks like this:

cache_dir aufs /export/vol01/cache 400000 64 64
cache_swap_low 97
cache_swap_high 99

Squid has consumed the entire partition:

/dev/dsk/c1t1d0s7 537G 529G 2.2G 100% /export/vol01

Not the 400GB expected in the cache_dir directive and is now giving
write failures.

Have I set something up wrong? Why has the cache_dir size directive been
ignored and why isn't old cached content being released?

-mikep