At the Hbase vs Accumulo deathmatch the other night Todd elucidated that Hbase's write-ahead log is in HDFS and benefits somewhat thereby. He neglected to mention that for years until HDFS append() was available Hbase just LOST data while Accumulo didn't .. but he was talking about the current state of affairs so, whatever.
The question now is, does it make any sense to look at HDFS as a place to store Accumulo's write-ahead log? I remember that BigTable used two write streams (each of which is transparently replicated by HDFS) and switched between them to avoid performance hiccups, so it does sound like a critical part of the overall performance. Such a big change would belong probably in 1.6 or later ... But there may be reasons to never use HDFS and to always use a separately maintained subsystem. Any one care to lay out the arguments for staying with a separate subsystem? I think we know the arguments for using HDFS. Aaron
