made an 8GB cache partition, and am using the standard Linux init script options of "-fakestat -stat 4000 -dcache 4000 -daemons 6 -volumes 256 -files 50000".
The default chunksize of 2^16 is 64k.64k * 50000 cache files is 3276800000 bytes, which is close to what you topped out at.
you need to increase -chunksize or -files (since your files are large, increasing chunksize is reasonable.)
Turns out it's a problem with the kernel module using 32 bit ints for calculations that determine when to trim the cache. I have patches against the 1.2.13 Linux module which ups the effective cache limit to about 80GB if you're interested.
Note that the number in the 32bit int is a count of 1k blocks, not bytes. The way that some of the integer math is done on afs_cacheBlocks means that you would not be able to use the full 32 bits, but even that should work up to around 20GB or so.
p7sPzttvS4FiC.p7s
Description: S/MIME cryptographic signature
