On 12/11/24 4:21 AM, Bart Van Assche wrote: > On 12/10/24 2:58 AM, hch wrote: >> On Tue, Dec 10, 2024 at 08:05:31AM +0000, Johannes Thumshirn wrote: >>>> Generally agreeing with all you said, but do we actually have any >>>> serious use case for cross-LU copies? They just seem incredibly >>>> complex any not all that useful. >>> >>> One use case I can think of is (again) btrfs balance (GC, convert, etc) >>> on a multi drive filesystem. BUT this use case is something that can >>> just use the fallback read-write path as it is doing now. >> >> Who uses multi-device file systems on multiple LUs of the same SCSI >> target ơr multiple namespaces on the same nvme subsystem? > > On Android systems F2FS combines a small conventional logical unit and a > large zoned logical unit into a single filesystem. This use case will > benefit from copy offloading between different logical units on the same > SCSI device. While there may be disagreement about how desirable this > setup is from a technical point of view, there is a real use case today > for offloading data copying between different logical units. But for F2FS, the conventional unit is used for metadata and the other zoned LU for data. How come copying from one to the other can be useful ? > > Bart. > -- Damien Le Moal Western Digital Research
