Where am I?

When AWS EC2 tells you that "requested instance type (cc1.4xlarge) is not supported in your requested Availability Zone (us-east-1b)", what they really mean is that you are using the wrong AMI. Switch to an HVM AMI. This enables support within Xen for Hardware Virtual Machine (HVM), using AMD SVM or Intel VT-x instructions.

Tomorrow's event prodded me into setting up IPv6 at home, where I use openwrt. The tutorial I found was helpful: I just had to change the interface names. On my system eth0.1 was eth1, and 6rdtun was called 6to4. Comcast's test page says I'm up and working. I can see the unicorn too.

Visit to ipv6-test.net for more tests.

Part 5 in a series by Mel Gorman describes how to measure the potential benefit from hugepages. The results match up reasonably well with CPU-intensive synthetic benchmarks on linux, which tend to show 10-15% improvement over ordinary pages.

The larger impact may be to application environments under heavy memory pressure. The OS can swap everything else out, but hugepage allocations are pinned. This is a double-edged sword. Preventing swapping may benefit some environments (cf vm.swappiness). But imagine a situation where you have 8-GB RAM and designate 4-GB for huge pages, but only use 2-GB. Now the OS has only 4-GB to manage, and the free 2-GB in huge pages are effectively wasted. If the system comes under memory pressure, that could lead to swapping or activate the OOM killer.

It wasn't rocket surgery, but blakeley.com now has an IPv6 stack and an AAAA record. If http://ipv6-test.com/validate.php can be believed, it even works. I had more trouble finding a server-side test tool than I had with the configuration.

I noticed this in the github pull requests for homebrew, and thought it looked interesting. We've all written a script that sends a command-line out to N hosts, right? Dancer's Shell looks like a nice way to automate that. It lets you place hosts in groups, and send commands to a group of hosts. The next time I need to work with a cluster, I'm planning to delve into this and see if it helps.