????????Figure 3??I/O??????????????????????????С??????????Ρ??????????????I/O?仯??????????????????????????????洢????????д?????cold data(?2/3)????????????hot/cold???????洢??

????????????HBase stack??logging/compaction/replication/caching????дI/O??????????????????????HBase????????????I/O??д???????????

????FM????????????????С

????FM????????????????Table 2??????????????????????????HBase?????RegionServer??????column family????????????HFile?????FM??????8??column family?????????column family?洢?????????????С?????????????column family???д?????????????????????????д??????????????cache all writes???????ò???(Figure 4)??

???????????column family???????90%??С??15M???????????????????????????column family??????????С??????MessageMeta???column family??????????С??293M??????Щ???????????????????????FM??????洢??large??long-lived files???????????????small?? short-lived?????HDFS??NameNode????????????????HDFS????????????洢????????????????????е?????????????洢??NameNode??????е????????NameNode federation??

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

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

????73.7%????????????????Σ?????1.1%????????????????64?Ρ????????????????????????????????????I/O????????19%??????????????????????ε????????????I/O??????Щ???????

??????HDFS?????FM?????????б????sequentiality????????high-bandwidth?? high-latency???е????????????????????洢????????????????????б????spatial locality??????I/O??????????á?