Hi Yuta, Thanks for starting this thread. I started looking into this issue and found out that retype+migration already provides a way to copy the data sparsely (with dd). The only issue was it wasn't enabled in the RBD driver which I did with this patch[1] (more details in commit message). If possible, can you try out the patch in your deployment and report if it fixes the issue you are experiencing? [1] https://review.opendev.org/c/openstack/cinder/+/954217 Thanks Rajat Dhasmana On Mon, Jul 7, 2025 at 2:19 PM Yuta Kambe (Fujitsu) <yuta.kambe@fujitsu.com> wrote:
Hi Eugen,
Thank you for your reply. I've confirmed that 'rbd sparsify' can increase available space.
However, I believe there's room for improvement in the retype implementation.
Currently, retyping between Ceph backends causes zero-filling, which unnecessarily consumes time and storage space. This is likely to happen frequently, for example, with retypes between Ceph's HDD and SSD backends, and the Ceph administrator would need to run 'rbd sparsify' frequently.
Are there any improvements to the retype implementation being considered in the community? I would also appreciate hearing your opinion on the need for improvement.
Best regards,