[Libguestfs] virt-v2v slow when running inside the VM

[Richard W.M. Jones]

On Fri, Apr 12, 2019 at 05:47:55PM -0700, Sureshkumar Kaliannan wrote:
> Bulk of the write to the "-sda" file completed within 15-20 mins although
> sshd/qemu-img receives constant stream of data from the nbd-server
> I'm not sure if this is because of "sparseness" (Not sure if the
> sparsifying is handled on the nbd-server side or on the receiving side)

Hard to say what's going on, but I can tell you about sparseness.

If all of the following apply:

 - it's Windows >= Vista / 7

 - you use the default partition alignment chosen by Windows at
   install time

 - the Windows disk contains mainly regular filesystems, not
   raw/unused/data partitions, and not Dynamic Disks

 - you're using not ancient ntfs-3g[1]

then virt-v2v is able to skip reading all sparse / unused / deleted
parts of the Windows disk.  It should skip over them immediately --
ie. nothing needs to read them at all.

Rich.

[1] https://www.mail-archive.com/ntfs-3g-devel@lists.sourceforge.net/msg01060.html

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