I wrote a tool called virt-sparsify which runs fstrim on disks via qemu. My colleague asked me a good question: Is this safe if qemu is killed (^C)? Could it corrupt the guest?
Using 'virt-sparsify --inplace disk.img' is essentially equivalent to doing: qemu-kvm \ -kernel <recent-kernel> \ -drive file=disk.img,discard=unmap,[virtio-scsi] \ -drive file=appliance And in the appliance doing: foreach fs in filesystems: mount -o discard fs /sysroot fstrim /sysroot umount /sysroot sync poweroff I think the answer is "safe", as long as the Linux kernel and qemu are written carefully, but it would be good to get an expert opinion. It looks like fstrim just sends discard requests. And mount/umount should be safe by the usual rules of journalling. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-top is 'top' for virtual machines. Tiny program with many powerful monitoring features, net stats, disk stats, logging, etc. http://people.redhat.com/~rjones/virt-top