Zach Shepherd's WordPress Blog

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Friday, October 5, 2007

Migration to AoE

I’ve finally gotten around to making it happen. I thought it was going to be painful, but it actually wasn’t bad. It was just a matter modprobing aoe and dm-multipath (and adding them /etc/modules), changing the masterlist on animal, and exporting them using vblade daemon.

I only ran into one issue: in the process of changing over to AoE, I started two images (comm and storage) on a blade (0010) that only had 896MB of memory for the dom0, bringing the memory for the dom0 to 640MB (each image used 128MB). I then shut down the two images, and started a different image (cosi). I thought the other two images had fully shutdown, but apparently I jumped the gun. This lowered the memory for the dom0 to 128MB (cosi uses 512MB). You’d think xen would give the dom0 the extra 256MB of memory (from the shutdown of comm and storage), but it looks like it just sets it aside. Since I don’t know enough about xen to know if there was a command to get the memory back and the dom0 was running dangerously slowly, I decided that it might be a good idea to get the memory back before the network (and network mounted images for the vms) timed out, so I did the only thing I knew would work: a reboot. It’s probably not the best solution, but it worked.

Now everything is set (including AoE on 0001) and I was able to reproduce the ‘issue’ of xen taking memory away from the dom0 when a vm was started, but just setting it aside (for use by other images if you create them) when the vm is shut down. If anyone knows anything about getting the memory back (or why the memory can’t be returned), I’d be interested in hearing about it.

posted by Zach at 7:24 pm  

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