[kiwijamo]

This is similar to AWS S3 object storage -- AWS has over the years changed how they store their S3 data -- however as long as the API responds the same way every time it's all good. Personally I would probably do some A/B testing -- migrate half the workload and compare A to B to see if the new system is performing better before migrating the other half.

[cyberax]

No, it's not. S3 has a very well defined API with easily measureable performance parameters. So AWS updates can make sure they don't make things worse.

This is not possible with a client's workload unless you can actually test it. That's why AWS will warn you multiple times if they need to migrate your EC2 instance onto a different hardware node. Even if it is technically "better".

Of course, the fact that clients trust their workloads to this guy probably means that there was nothing important there.

[hedora]

The author also converted some of these VMs to jails, so I assume they have root on the VMs (and the customers want them to admin the host). That means they should be able to see the application level performance metrics.

[cyberax]

Yeah, so he got surprised when his customer mentioned how their workloads became faster.