32MB is what they tested on the article.

To clarify a little on what’s happening here, they’re not using the v-cache as a memory space and making the volume there as you might create a partition on a conventional disk drive, but rather, they’re accessing the ramdisk in such a way as to trick the system into keeping that it in cache. It’s almost completely impractical in real terms, but it’s a fun way to exploit the cache algorithm to get some silly numbers out of it.