Re: [Qemu-devel] TRIM, UNMAP and QCOW2 release of block information - Thin provisioning

[Stefan Hajnoczi]

On Sun, Aug 12, 2012 at 8:00 PM, Gerhard Wiesinger <address@hidden> wrote:
> As far as I saw QEMU/KVM supports the trim command on IDE/SATA devices and
> the UNMAP command on SCSI devices/disks (thanks Paolo Bonzini). Will the
> qcow2 format (or other formats) use this information and also release the
> blocks for thin provisioning to save disk space on filesystems?
>
> VirtualBox also has such a feature in the new beta version:
> http://www.fb-developers.info/blog/2012/virtualbox-v4-2-is-coming/

This has recently been discussed, please search the list for more info
from Kevin Wolf or Paolo Bonzini.

qcow2 marks the discarded blocks as free and will reuse them in future
allocations.  It does *not* discard at the OS level.

For raw files you can get discard to work on an xfs host file system.
In the future ext4 support can also be added.

Stefan