VMworld Video: VMware FT and PerformanceDate: Feb 25, 2009
This session discusses the affect that VMware FT has on performance. 3 main things – firstly, you can only current protect a 1xVCPU VM with FT. Given that one way to improve performance is add more vCPU that needs to be kept in consideration. Currently CPUs don’t really have a hook to allow VMware to track the memory changes of two vCPUs – whereas the “lockstep” attribute on most modern CPUs do allow this for single vCPUs.
Secondly, latency is the key – the gap between the Primary VM and Secondary VM because the Primary VM cannot massively go quicker than its secondary. Whilst latency is small for outbound traffic (because that is not replayed in the secondary) high amounts of inbound network traffic can have significant impacts.
Thirdly, I/O bound VMs for storage may need switching to secondary method which in test didn’t out perform the default method – this secondary method is labelled as “shared read mode"