Indeed, I didn't look at latency. For time sync, I got sub-millisec syncs after using Ariel's tip at http://www.afewmoreamps.com/2011/07/configuring-ntp-for-vo

Indeed, I didn't look at latency. For time sync, I got sub-millisec syncs after using Ariel's tip at http://www.afewmoreamps.com/2011/07/configuring-ntp-for-voltdb.html http://www.afewmoreamps.com/2011/07/configuring-ntp-for-volt... . Essentially, switching NTP off and manually running ntpdate -p 8 <server name> repeatedly can give you that. Just do it ten times in a row - I don't know why the normal operation of NTP doesn't achieve the same. This tight sync seemed to increase throughput by 2%. Because that was not so significant I did not further investigate the consequences of good or bad time syncing. The time sync that EC2 instances come with out of the box seemed to sometimes be good enough to run multiple VoltDB hosts without any additional syncing, sometimes not, and it seemed to vary quite a bit over time. So really you must deal with NTP in EC2, but of course you need NOT get the sync to sub-millisecond values.