v0.85
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* The client-side caching for librbd is now enabled by default (rbd
  cache = true).  A safety option (rbd cache writethrough until flush
  = true) is also enabled so that writeback caching is not used until
  the library observes a 'flush' command, indicating that the librbd
  users is passing that operation through from the guest VM.  This
  avoids potential data loss when used with older versions of qemu
  that do not support flush.

    leveldb_write_buffer_size = 32*1024*1024  = 33554432  // 32MB
    leveldb_cache_size        = 512*1024*1204 = 536870912 // 512MB
    leveldb_block_size        = 64*1024       = 65536     // 64KB
    leveldb_compression       = false
    leveldb_log               = ""

  OSDs will still maintain the following osd-specific defaults:

    leveldb_log               = ""

v0.86
-----