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Asynchronous AOF fsync is taking too long (disk is busy?). Writing the AOF buffer without waiting for fsync to complete, this may slow down Redis.

To me this indicates something else is up. What other IO workloads are on the server? How fast are things changing the redis instance (as the fsync should only have to commit the lines that were added since the last one).

Also never fsyncing won't make things slower, it will just make things less durable as the last x operations may be lost if you lose power and the changes haven't been fsynced.

It's hard to say what's going on on the system. If I change appendfsync to no, the system runs happily, but the moment I turn it to everysec fsync starts taking too long.

Also appendfsync no doesn't really mean never, it still fsync's but only once a minute or 30 seconds, as often as OS permits.

What could I be looking at iostat, iotop, any other recommendations? BTW, your quick response is HUGELY appreciated.

Grrrr.... after all hopeless attempts to identify the problem I contacted Rackspace and they said we had 2 noisy neighbors and kicked them out for us.

Frustrating, time to make redis a less SPOF component.

Thanks for responding!