Azure requires disks to be fixed-size VHD files when uploading to blob storage
in order to create image/gallery objects from them. This is documented here[1].
To prevent mistakes from happening create disks in that format directly so that
any azure compatible tool can upload them, though azcopy is recommend because
it handles their sparseness best.
This has not been an issue for us so far because kola uses code from an older
utility that transparently handled the dynamic-to-fixed-size conversion for VHD
files (azure-vhd-utils). But people working with these things for the first
time fall into this trap.
[1]: https://docs.microsoft.com/en-us/azure/virtual-machines/linux/create-upload-generic#resizing-vhds.
Signed-off-by: Jeremi Piotrowski <jpiotrowski@microsoft.com>
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