We have a ticket open for this: https://issues.apache.org/jira/browse/CASSANDRA-809
Ideally I think we'd like to leave the node up to serve reads, if a disk is erroring out on writes but still read-able. In my experience this is very common when a disk first begins to fail, as well as in the "disk is full" case where there is nothing actually wrong with the disk per se. On Wed, Apr 21, 2010 at 9:08 AM, Oleg Anastasjev <olega...@gmail.com> wrote: > Hello, > > I am testing how cassandra behaves on single node disk failures to know what > to > expect when things go bad. > I had a cluster of 4 cassandra nodes, stress loaded it with client and made 2 > tests: > 1. emulated disk failure of /data volume on read only stress test > 2. emulated disk failure of /commitlog volumn on write intensive test > > 1. On read test with data volume down, a lot of > "org.apache.thrift.TApplicationException: Internal error processing get_slice" > was logged at client side. On cassandra server logged alot of IOExceptions > reading every *.db file it has. Node continued to show as UP in ring. > > OK, the behavior is not ideal, but still can be worked around at client side, > throwing out nodes as soon as TApplicationException is received from > cassandra. > > 2. Much worse was with write test: > No exception was seen at client, writes are going through normally, but > PERIODIC-COMMIT-LOG-SYNCER failed to sync commit logs, heap of node quickly > became full and node freezed in GC loop. Still, it continued to show as UP in > ring. > > This, i believe, is bad, because no quick workaround could be done at client > side (no exceptions are coming from failed node) and in real system will lead > to > dramatic slow down of the whole cluster, because clients, not knowing, that > node > is actually dead, will direct 1/4th of requests to it and timeout. > > I think that more correct behavior here could be halting cassandra server on > any > disk IO error, so clients can quickly detect this and failover to healthy > servers. > > What do you think ? > > Did you guys experienced disk failure in production and how was it ? > > >
