Alex Hopmann’s Blog

So Windows (like most OSes) maintains a number of caches where it keeps in RAM frequently accessed disk contents (as well as a few other things). Normally these are not adjustable- it just uses extra free memory for this to improve performance, and the minute you actually need the memory, it is freed up and available to a real program.

Hyper-V puts a little twist in this. When you create or start up a new VM, it needs the full memory as hard-allocated memory to that VM and apparently it doesn’t force a cache clear if there isn’t enough memory available. We are building a bunch of stuff on 48GB servers and initially thought we would easily be able to put 3x 15GB VMs on them- the remaining 3GB would be plenty for the OS that basically wasn’t doing anything. But at times we have found the Cached memory is as high as 20GB (after a bunch of big file copies, usually of VHD images), and the machine doesn’t have enough free RAM to boot the target VMs.

Any thoughts on how we can clear this? Dynamic memory coming in future releases should fix this issue, but for now it would be great if we could just run a cache clear/flush right before VM start time.

Last weekend we headed down to Northern California to do Tough Mudder. Six months ago when we signed up for this it sounded like a great idea. As the event day got closer and closer the Tough Mudder guys kept sending email updates about how hard-core this event is. To be honest I was starting to dread it. My overall fitness is ok (I ran the Bellingham half-marathon a couple of weeks ago) but I hadn’t been doing my pushups and was pretty sure climbing over a 12′ wall sounded impossible.

Getting to the event via AlexAir was perfect. Rather than flying into Sacremento which is over 3 hours drive away we flew into Calaveras County airport which was less than an hour from the site. Calaveras (KCPU) is a classic wonderful small airport with friendly FBO with a loaner-truck, nice gas prices, a great runway and all.

We lucked out and event day weather was great. Not too cold, not too hot. We started a bit after noon, shouted our Tough Mudder pledge and started on the course. In the end it wasn’t so bad- going up and down the mountain twice at altitude was exhausting, but the obstacles weren’t as bad as I feared. There tended to be foot holds, the wall wasn’t straight up, an the bus you had to climb over had a net.

Tough Mudder isn’t officially timed. It is more about teamwork and it was sweet to have a great team. Overall a really fun event.