dynamic_snitch=true is the default. So it is usually on "wrapping" other snitches. I have found several scenarios where it does not work exactly as your would expect.

On Fri, Mar 8, 2013 at 2:26 PM, Hiller, Dean <Dean.Hiller@nrel.gov> wrote:
Our test setup

4 nodes, RF=3, reads at CL=QUOROM and we tried CL=TWO
Tell the network card to slow down every packet on node 2
After fixing astyanax to not go to node 2 anymore, we are still seeing cassandra have issues as it seems to be involving node 2 somehow.  If we take node 2 down, it all speeds back up.

We are trying to get this working such that a slow node in cassandra does not impact our customers.

We are in 1.2.2 and added the following properties….(our properties show PropertyFileSnitch though I see the keyspace has org.apache.cassandra.locator.SimpleStrategy set probably because it was created through a tool instead of CLI…shucks)….anyways, I still expected dynamic snitch to work….

# controls how often to perform the more expensive part of host score
# calculation
dynamic_snitch: true
dynamic_snitch_update_interval_in_ms: 100
# controls how often to reset all host scores, allowing a bad host to
# possibly recover
dynamic_snitch_reset_interval_in_ms: 600000
# if set greater than zero and read_repair_chance is < 1.0, this will allow
# 'pinning' of replicas to hosts in order to increase cache capacity.
# The badness threshold will control how much worse the pinned host has to be
# before the dynamic snitch will prefer other replicas over it.  This is
# expressed as a double which represents a percentage.  Thus, a value of
# 0.2 means Cassandra would continue to prefer the static snitch values
# until the pinned host was 20% worse than the fastest.
dynamic_snitch_badness_threshold: 0.1

Any help appreciated,