?????????????cache????????????Flash???дbuffer????????????????????????HDFSд???????????DataNode????????????б????????(??????DataNode???洢???????????DataNode?????flush??????????????????DataNode?????)????????Flash??дbuffer?????????????????дbuffer????????compaction???????????????????I/O???????????????????????????????????????????????????Flash??дbuffer??á?

?????????????????????????洢??м???Flash?????????治?????????????3?????????????????5%???????????????????(????о??е???SSD??????)??

????2.?????????????????

??????Figure 16???????????????????????????Σ?db layer/replication layer/local layer????????????????????????????????????????db layer????????DB?????????????洢?????available??reliable???

????HBase?????a)???????????????replication??HDFS??????????????????????????????compaction??????????????????С????????merge-sorting?????????????????????????????????е????RS/DN???????????????RS/DN????????д??????????紫??I/O??

???????b)???????replication??????DB??????棬Facebook?????????Salus?????????????????????????????Cassandra????????????????????????DB??????????????????????????????????????DB??Э????￡?????????