Originally our osd tree looked like this: ID  CLASS WEIGHT     TYPE NAME                     STATUS REWEIGHT PRI-AFF  -1       2073.15186 root default -14        176.63100     rack s01-rack -19        176.63100         host s01 <snip osds> -15        171.29900     rack s02-rack -20        171.29900         host s02 <snip osds> etc. You get the idea. It was a legacy thing as we've been upgrading this cluster since probably firefly, and started with way less hardware. The crush rule was set up like this originally:         step take default         step chooseleaf firstn 0 type rack which we have modified to         step take default         step chooseleaf firstn 0 type host taking advantage of chooseleaf's behavior (eg searching in depth instead of just a single level). Now we thought we could get rid of the rack buckets simply by moving the host buckets to the root using "ceph osd crush move s01 root=default", however this resulted in a bunch of data movement. Swapping the IDs manually in the crushmap seems to work (verified via crushtool's --compare), eg. changing the ID of s01 to s01-rack's and vice versa, including all shadow trees. Looking around I saw that there is a swap-bucket command but that does not swap the IDs just bucket contents, so would result in data movement. Other than manually editing the crushmap is there a better way to achieve this? Is this way the most optimal?

Could you elaborate a bit more? upmap is used to map specific PGs to specific OSDs in order to deal with CRUSH inefficiencies. Why would I want to add a layer of indirection when the goal is to remove the bucket entirely?

On 2019-09-01 05:57, Konstantin Shalygin wrote: Let's say with upmap I take the current mapping and "override" CRUSH, then remove the rack bucket and move the host directly to the root. And then what? We'd never, ever be able to go back, and what's worse, for any new expansions we'd need to manage the PG mappings manually. Unless I'm missing something, while this would solve the problem in the very very short term, it would create horrible issues down the line, and would be shooting ourselves in the foot as far as maintainability is concerned. As I've said we'd been rolling this cluster since at least Firefly, and I don't want to mess with it. The solution I've outlined in my original mail works (swapping the bucket IDs) and seems more maintainable, however, I've been wondering if the bucket types are just labels or do they have any other semantic meaning?