On Sun, Mar 28, 2010 at 05:18:03PM +0200, Diego Calleja wrote: > Hi, I'm using KVM, and the virtual disk (a 20 GB file using the "raw" > qemu format according to virt-manager and, of course, placed on a btrfs > filesystem, running the latest mainline git) is awfully slow, no matter > what OS is running inside the VM. The PCBSD installer says it's copying > data at a 40-50 KB/s rate. Is someone using KVM and having better numbers > than me? How can I help to debug this workload?
The problem is that qemu uses O_SYNC by default, which makes btrfs do log commits for every write. Once the O_DIRECT read patch is in, you can switch to that, or tell qemu to use a writeback cache instead. -chris -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
