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AWS and High-CPU Instances

Mon, 04 Jul 2011 09:52:16 UTC

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.

Intel SSD 510

Wed, 02 Mar 2011 07:41:06 UTC

Intel's latest SSD pricing isn't as much of a shift as I had hoped for. As I see it, they have gone from $2.75/GB to $2.50/GB for enterprise-class SSD devices, and capacities have grown to 230-GB per device. That's an improvement, and the performance looks good. The combination of SATA-3 and lower failure rates than consumer-grade SSD may also help justify the price.

While SSD is now the logical choice over 15k-rpm disks, very few deployments use those. Instead, 10k-rpm are the workhorse for disk-heavy enterprise applications. SSD is getting closer, but still costs at least twice as much. Brand-name 10k-rpm SATA disks are available for $0.72-$1 per GB, with capacities up to 600-GB per spindle. It will take a lot of performance-related pain to cross that gap.

LWN article on impact of hugepages

Tue, 22 Feb 2011 07:15:41 UTC

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.