On Sat, Jul 03, 2021 at 04:34:09PM +0300, Nir Soffer wrote: > For some reason I did not see this change in the mailing list: > https://github.com/libguestfs/virt-v2v/commit/18084f90d9dd9092831cb348703... I didn't post it ... However the commit on its own is correct because -oa preallocated was rejected with an error. But see below because I do intend to add the feature back (unbroken). > The commit message claims: > > > Using -oa preallocated with -o rhv-upload always gave an error. We > > should be able to implement this properly in modular virt-v2v, but as > > this option did nothing here remove it to simplify things. > > But I used -oa preallocated and -oa sparse and it worked fine after removing > the unhelpful validation, and using: > > sparse=params["output_sparse"] > > The code was already broken even before this change with block storage domain > (iSCSI/FC) and raw format (the default), since raw-sparse is not supported in > block base storage, but now there is no way to fix the code. > > We can always use qcow2-sparse - this combination is most useful in RHV > but using raw preallocated volume can give better performance or reliability > and this is still the default format for block storage RHV. > > Since RHV does not support the feature of selecting the image format and > allocation policy for the user, and does not make the available combinations > or the system defaults available via the API, virt-v2v must pass the decision > to the user of the program. In modular virt-v2v[1] we will be using nbdcopy to copy to a disk pipeline. For rhv-upload it will actually make no difference. It will work the same as current code, ie. nbdkit + python + rhv-upload-plugin. However I was actually thinking we could get nbdcopy to use the nbdcopy --allocated flag, essentially pushing zeroes (or hopefully NBD_CMD_WRITE_ZEROES commands not actual zeroes) through the pipeline. Now I think about it a bit more this seems like it's going to be somewhat inefficient as far as imageio is concerned.

We can certainly put the -oa flag back again, passing it through params["output_sparse"]. How does it fail if we select the wrong combination? - can we check it in precheck? Will there ever be a way of querying what combinations are supported?