[Qemu-devel] [Bug 1523246] Re: Virtio-blk does not support TRIM

[Stefan Hajnoczi]

While the Linux virtio-blk guest driver now supports discard and write
zeroes, QEMU's virtio-blk device emulation does not support it yet.

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https://bugs.launchpad.net/bugs/1523246

Title:
  Virtio-blk does not support TRIM

Status in QEMU:
  Confirmed

Bug description:
  When model=virtio is used, TRIM is not supported.

  # mount -o discard /dev/vda4 /mnt
  # mount | tail -1
  /dev/vda4 on /mnt type fuseblk 
(rw,nosuid,nodev,relatime,user_id=0,group_id=0,allow_other,blksize=4096)
  # fstrim /mnt/
  fstrim: /mnt/: the discard operation is not supported

  Booting without model=virtio allows using TRIM (in Windows as well).

  Full QEMU line:

  qemu-system-x86_64 -enable-kvm -cpu host -bios
  /usr/share/ovmf/ovmf_x64.bin -smp 2 -m 7G -vga qxl -usbdevice tablet
  -net nic,model=virtio -net user -drive discard=unmap,detect-
  zeroes=unmap,cache=none,file=vms/win10.hd.img.vmdk,format=vmdk,if=virtio

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