Distributed Parity Cache Table

Motivation Parity updating is a high cost operation  Especially for small write operations Read old data 、 Read Old Parity 、 write new data 、 write new parity Basic ideas  Delay the generation of parity Cached data could be used without reread Parity & newly written data could be cached for “the same” write Beyond parity?  A server-side cooperative cache

Distributed Parity Cache Table A whole stripe is more meaningful than partial blocks  Local file system cache knows nothing about a whole stripe Distributed parity cache table knows !! Small write phenomenon  Could aggregate small writes  Benefits from previous read Cooperative cache  PVFS does not provide cache

Architecture

Striping Size and Cache Blocks

Cache Block Each block contains 16K data bytes metadata  DTag : Data tag  PTag : Parity tag  LRef : # of hits in this block  GRef: # of hits in this stripe

Cache Replacement Algorithm IF PTag is null THEN IF Operation is READ THEN USE LRef Field & LRU ELSE IF Dirty bit is Set THEN Write the Parity Block and the replaced Block END IF Write Operation Proceed Update the PTag Field END IF ELSE IF PTag == itself.DTag and DTag != itself.DTag THEN Replace the block ELSE IF PTag != DTag USE LRef Field & LRU END IF

Performance Evaluation (1/4) – Native Calls

Performance Evaluation (2/4) – Native Calls

Performance Evaluation (3/4) – POSIX APIs

Performance Evaluation (4/4) – POSIX APIs