The solution to pricey DRAM is memcached for flash.
You can stuff your home system full of DRAM without putting a hurt on your bank account, but when you're talking about servers on the scale of what's needed to keep Facebook up and running, things tend to get expensive. It's for this reason that Facebook has decided to reduce its dependance on DRAM. In its place, the social networking site built a data cache that runs on flash memory.
It's called McDipper and it's a memcache-compatible flash-based cache server. The draw for Facebook is that flash provides up to 20 times the capacity per server and still supports tens of thousands of operations per second, so it's essentially a no-brainer.
"We serve over 150 Gb/s from McDipper forward caches in our CDN. To put this number in perspective, it's about one library of congress (10 TB) every 10 minutes. We do this with a relatively small set of servers, and we're very pleased with McDipper's performance on our CDN," Facebook explains .
According to Facebook, McDipper can reduce the number of deployed servers in some pools by as much as 90 percent while still delivering more than 90 percent of "get responses" with sub-millisecond latencies.