Eventually consistent unless you're only using a single node. I believe that Redis itself commits to disk at various checkpoints in time, so if a fail happens, you're really only guaranteed to fail over into a pool of data that's consistent up to the last checkpoint of the node you're moving to.
EDIT: And as antirez said above, you can WAIT to force synchronization to all nodes, so you would be pretty likely to fail over onto a node that has n-1 messages if it didn't sync in time. That still isn't guaranteed however.
EDIT: And as antirez said above, you can WAIT to force synchronization to all nodes, so you would be pretty likely to fail over onto a node that has n-1 messages if it didn't sync in time. That still isn't guaranteed however.