Re: [Qemu-devel] TRIM/DISCARD/UNMAP support on qemu-nbd

["Richard W.M. Jones" <rjones@redhat.com>]

On Tue, Jan 07, 2014 at 09:48:17PM +0100, Paolo Bonzini wrote:
> Il 07/01/2014 21:27, Richard W.M. Jones ha scritto:
> > Not much more what I said in the original email (especially see the
> > attached script which you can download from the bottom of this page:
> > https://lists.gnu.org/archive/html/qemu-devel/2014-01/msg00084.html )
> > 
> > Basically it tries to dd /dev/zero into the virtio-scsi device exposed
> > by qemu, then calls sg_unmap (there are two devices, it only unmaps
> > the first so we can hopefully see the difference), but it doesn't seem
> > to have any effect on the underlying file.  The underlying file is a
> > regular raw-format file on ext4.
> > 
> > I called sg_readcap/sg_vpd and we seem to have all the right
> > capability bits exposed.
> > 
> > This script won't work with regular libguestfs.  I compiled a special
> > appliance that had the sg tools included.
> 
> Try again with the pull request of
> http://permalink.gmane.org/gmane.comp.emulators.qemu/248421

No difference from before, as far as I can see.

Here is the output of sparsetest.sh:

0    /tmp/test1
0    /tmp/test2
Read Capacity results:
   Protection: prot_en=0, p_type=0, p_i_exponent=0
   Logical block provisioning: lbpme=1, lbprz=0
   Last logical block address=204799 (0x31fff), Number of logical blocks=204800
   Logical block length=512 bytes
   Logical blocks per physical block exponent=0
   Lowest aligned logical block address=0
Hence:
   Device size: 104857600 bytes, 100.0 MiB, 0.10 GB
Block limits VPD page (SBC):
  Write same no zero (WSNZ): 1
  Maximum compare and write length: 0 blocks
  Optimal transfer length granularity: 0 blocks
  Maximum transfer length: 0 blocks
  Optimal transfer length: 0 blocks
  Maximum prefetch length: 0 blocks
  Maximum unmap LBA count: 2097152
  Maximum unmap block descriptor count: 255
  Optimal unmap granularity: 8
  Unmap granularity alignment valid: 0
  Unmap granularity alignment: 0
  Maximum write same length: 0x0 blocks

16M	  /tmp/test1                   <--- note both file disk
16M	  /tmp/test2                   <--- usages are the same

Those are raw files on ext4.  I'll try qcow2 and follow up.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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