Apache Reference: mod_proxy, CacheSize
Maximum Disk Space Used for the Proxy Document Cache
Syntax: CacheSize A
Example: CacheSize 1024
Since: Apache 1.1
This directive sets the maximum disk space used by the document cache
in Kilobytes. Although usage may exceed this
setting, the garbage collection will subsequently delete files until the
usage is at or lower than this size. Depending on the expected
proxy traffic volume and CacheGcInterval, use a value that
is at least 20\% to 40\% lower than the available disk space.