????????Figure 3??I/O??????????????????????????小??????????巍??????????????I/O?浠�??????????????????????????????娲�????????写?????cold data(?2/3)????????????hot/cold???????娲�??

????????????HBase stack??logging/compaction/replication/caching????写I/O??????????????????????HBase????????????I/O??写???????????

????FM????????????????小

????FM????????????????Table 2??????????????????????????HBase?????RegionServer??????column family????????????HFile?????FM??????8??column family?????????column family?娲�?????????????小?????????????column family???写?????????????????????????写??????????????cache all writes???????貌???(Figure 4)??

???????????column family???????90%??小??15M???????????????????????????column family??????????小??????MessageMeta???column family??????????小??293M??????些???????????????????????FM??????娲�??large??long-lived files???????????????small?? short-lived?????HDFS??NameNode????????????????HDFS????????????娲�????????????????????械?????????????娲�??NameNode??????械????????NameNode federation??

????FM???????I/O????????

?????????temporal locality?? spatial locality?? sequentiality??????????

????73.7%????????????????危?????1.1%????????????????64?巍????????????????????????????????????I/O????????19%??????????????????????蔚????????????I/O??????些???????

??????HDFS?????FM?????????斜????sequentiality????????high-bandwidth?? high-latency???械????????????????????娲�????????????????????斜????spatial locality??????I/O??????????谩?