I’m at the SNIA Symposium this morning. Hence the short post.
What is the impact of virtual machines on I/O?
Engineers have spent decades optimizing the OS, drivers, caching, controllers and disks for specific workloads.
Observed behavior such as locality of reference have informed many strategies. Like read-ahead.
But when you put 25 virtual machines on a single server, what happens to all this hard-won empiricism? It’s gone.
Each of the 25 machines may have predictable I/O behavior. But together all those I/O patterns smear together. One I/O may have nothing to do with the next 10.
Fast and stupid
That puts a premium on stupid, but fast storage. Storage that doesn’t think about what you may be trying to do because you aren’t trying to do anything. A jumble of VMs is doing it.
The StorageMojo take
The “stupid vs smart” network debate has been around for decades. In storage we’ve always taken it for granted that smart is better. But now?
Not so much.
Comments welcome, of course. If you are running a lot of VMs what I/O issues have you noticed?