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The experiments are conducted on IBM HS21 blades connected by 1Gb Ethernet. Each blade has two 2.33GHz Intel Xeon 5148 CPUs and a 70GB hard drive (model MAY2073RC). The host OS is Ubuntu 10.04 (Linux kernel 2.6.32-21), and uses either ext4 or a logical volume to store an image. The guest OS is Ubuntu 9.0.4 (Linux kernel 2.6.28-15), and uses ext4 to store PostMark data. The evaluated version of QEMU is the development code checked out from git.qemu.org/qemu.git at the beginning of January, 2011 (a minor bug in that development version was fixed so that qemu-img could create images larger than 2GB on a 32-bit platform). QEMU is configured with --enable-kvm, virtio, and cache=none. The base image is 1GB. The copy-on-write FVD or QED image is 50GB. A FVD or QED image is stored on the local disk of a blade W. The base image is stored on another blade Z and accessible to blade W through NFS. PostMark runs in a VM and works on about 42GB data. One run of PostMark takes about 4 to 8 hours to finish, depending on the image format. Before collecting numbers for each run, both the host ext4 and the guest ext4 are reformatted to avoid interference from previous runs. PostMark uses the following configuration:

set size 10000 50000
set number 1500000
set transactions 100000
set buffering false   # Use read()/write() instead of fread()/fwrite()