[Libguestfs] Question about mounting QCOW2 files....

[Richard W.M. Jones]

[Adding libguestfs mailing list]

On Sun, Oct 14, 2018 at 11:53:17AM -0400, Raghuram Devarakonda wrote:
> Hi,
> 
> My name is Raghuram Devarakonda and I am a big fan of "nbdkit". I have
> successfully used it to prototype (using Python plugin) a complex
> project in our company and since then, I have also been trying to
> understand and learn "guestfs-tools" as well. I have a question in
> this regard and I hope you don't mind my sending mail gratuitously.
> 
> In our project, we deal with quite large sparse files whose total size
> runs into several hundred terabytes or even more, though actual
> allocated size on disk is much smaller. The problem is that such large
> files present issues for copying around, compression, or even for
> computing checksums. I am wondering of I can use guestfs-tools to
> mount a QCOW2 image and then use the image as sparse file. The idea is
> that actual file on the disk would be compact though to our code,
> sparse file interface is preserved.

It's not very clear to me exactly what you want, but in general yes
qcow2 is a good way to handle very large, sparse disk images.

If you can be clearer about exactly what you mean by "mount" then I
could answer the question better.  For example, do you mean "mount a
filesystem in the qcow2 image"?  In which case use guestmount.  If you
mean "attach the qcow2 disk as a local device" then qemu-nbd can do
this.

Rich.

> Can you please let me know if this is possible? Can I mount a sparse
> file using guestfs-tools even though it is not really a disk?
> 
> Thanks in advance,
> Raghu

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