just following up on this thread because it was the most cromulent when I was searching.
I’ve been working on migrating to new disks, and the old disks are btrfs, and it’s been totally the wooorrrssst
The first drive had 2.5tb of storj data on it. The initial copy took two weeks. The btrfs source disk was only showing about 2MB/s of read performance while simply traversiing the file tree looking for files to copy. Then when real files were being transferred the performance fluctuated between 2MB/s and 6MB/s. At the tail end there were some bigger spikes in speed, but it was mega slow. Then the final --delete rsync took about a day.
The second drive has 5.5tb of data. I used the long wait time to “prepare” it as much as possible. Did a btrfs defrag, made sure the noatime attribute was set on every file (as well as drive mount options), switched the btrfs metadata from dupe to single (no idea if this really changed anything). And it was still mega slow, but not quite as bad. The initial copy of 5.5 tb took about a week.