I'm trying to get fstrim in a guest to cause the host disk to become sparse, without success so far. I wonder if anyone can see what I'm missing?
Guest: - guest kernel: 3.13.4-200.fc20.x86_64 - ext4 guest filesystem - fstrim from util-linux 2.24.1 - cat /sys/block/sda/device/scsi_disk/*/provisioning_mode unmap Qemu: - qemu from git today (e9d818b8b1a) - Drive uses virtio-scsi - Drive uses discard=unmap /home/rjones/d/qemu/x86_64-softmmu/qemu-system-x86_64 -L /home/rjones/d/qemu/pc-bios -global virtio-blk-pci.scsi=off -nodefconfig -enable-fips -nodefaults -display none -machine accel=kvm:tcg -m 500 -no-reboot -rtc driftfix=slew -no-hpet -global kvm-pit.lost_tick_policy=discard -kernel /home/rjones/d/libguestfs/tmp/.guestfs-1000/appliance.d/kernel -initrd /home/rjones/d/libguestfs/tmp/.guestfs-1000/appliance.d/initrd -device virtio-scsi-pci,id=scsi -drive file=/home/rjones/d/libguestfs/test1.img,cache=writeback,discard=unmap,format=raw,id=hd0,if=none -device scsi-hd,drive=hd0 -drive file=/home/rjones/d/libguestfs/tmp/.guestfs-1000/appliance.d/root,snapshot=on,id=appliance,cache=unsafe,if=none -device scsi-hd,drive=appliance -device virtio-serial-pci -serial stdio -device sga -chardev socket,path=/home/rjones/d/libguestfs/tmp/libguestfsSwrSCg/guestfsd.sock,id=channel0 -device virtserialport,chardev=channel0,name=org.libguestfs.channel.0 -append "panic=1 console=ttyS0 udevtimeout=600 no_timer_check acpi=off printk.time=1 cgroup_disable=memory root=/dev/sdb selinux=0 TERM=xterm-256color" Host: - host kernel: 3.12.5-302.fc20.x86_64 - ext4 host filesystem - backed by m-SATA SDD Methodology: (0) Observe the file size on host: $ ls -ls test1.img 0 -rw-rw-r--. 1 rjones rjones 1073741824 Mar 10 16:08 test1.img ^ +---- sparse file, 0 blocks used (1) Create an ext4 filesystem on /dev/sda in the guest. (2) Create a big data file of random data (10 MB) & sync. (3) Observe the file size on the host: $ ls -ls test1.img 59804 -rw-rw-r--. 1 rjones rjones 1073741824 Mar 10 16:09 test1.img (4) rm /data in guest (5) fstrim / in guest [actually, I do this several times] (6) sync (6) Observe the file size on host: $ ls -ls test1.img 59804 -rw-rw-r--. 1 rjones rjones 1073741824 Mar 10 16:10 test1.img Unchanged! I'm expecting the first number (59804 blocks) to get substantially smaller. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones virt-df lists disk usage of guests without needing to install any software inside the virtual machine. Supports Linux and Windows. http://people.redhat.com/~rjones/virt-df/
