Ceph

See Jim's patch on the ML. Need to tune leveldb parameters, but only for monitor, and in the ctor (says sam?).

While we're at it, though, let's add parallel tunables for the OSD, and probably increase the cache size there.

Preliminary branch in wip-leveldb-config. Going to do some brief tests around it to look at resource consumption.

Initially though I just want to make the minimal set of changes he needed so it would run — we have not in the past enabled any caching whatsoever, and it's not really necessary since it's over and above what the page cache already does.

Okay, these defaults at least don't balloon memory usage at startup, and they look comparable when doing comparable activities. More specific tests than that will need to be done by somebody else.

Got reviews from both of them and Sage. Pushed a new version which uses "leveldb" instead of "ldb" in the config names that should be ready for merge (although still waiting on more testing).

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