On Mon, Oct 15, 2018 at 3:54 AM Richard W.M. Jones <rjones(a)redhat.com&gt; wrote: > > [Adding libguestfs mailing list] > > On Sun, Oct 14, 2018 at 11:53:17AM -0400, Raghuram Devarakonda wrote: > > Hi, > > > > 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. We would like to create and write to a large sparse file but would like to keep the file on disk itself in compact format. So we are not talking about a file system but a single file. I guess this means creating qcow2 disk and attach as a local device?