There is a very corner case when bad things could happen(ie data loss):
1) RS #1 is going to roll its HLog - not yet created the new one, old one will get no more writes
2) RS #1 enters GC Pause of Death
3) Master lists HLog files of RS#1 that is has to split as RS#1 is dead, starts splitting
4) RS #1 wakes up, created the new HLog (previous one was rolled) and appends an edit - which is lost
The following seems like a possible solution:
1) Master detects RS#1 is dead
2) The master renames the /hbase/.logs/<regionserver name> directory to something else (say /hbase/.logs/<regionserver name>-dead)
3) Add mkdir support (as opposed to mkdirs) to HDFS - so that a file create fails if the directory doesn't exist. Dhruba tells me this is very doable.
4) RS#1 comes back up and is not able create the new hlog. It restarts itself.