I was playing around with a EC2 instance, and I got this great idea that I should benchmark the disk subsystem. I had expected pretty standard performance for the disk at /mnt, but I was wrong:
Benchmarking /dev/sda1 [1537MB], wait 30 seconds
Results: 1014 seeks/second, 0.99 ms random access time
Benchmarking /dev/sda2 [152704MB], wait 30 seconds
Results: 4494 seeks/second, 0.22 ms random access time
Thats pretty damn fast. To get this sort of performance out of a RAID-5 set I think you need a hole lot of disks, maybe 20 or so? It sure as hell beats any disk I have at home with a factor of about between 15 and 60.
I don't know if this could be a Xen problem with this particular benchmark, but if it is true I actually just found a use for EC2: to run my DB-intensive information extraction jobs on. Though they are still most likely better solved by just buying a new machine with 4 or 8GB of RAM. It is pretty cheap now.
Edit: Oh, yeah, I understand that this disk array is shared by a number of instances. A good question then is by how many? And how likely are people to actually use the disk for any stressful activity, with it being non-persistent and all?
Edit2: Oh yes, I am stupid. This is most likely due to Xen using a sparse Copy-on-Write format disk image? It would explain it all, hitting the same physical sector over and over....
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