Hi, I have an old Mimic cluster that I'm doing some cleanup work on and adding SSDs, before upgrading to a newer version. As part of adding SSDs, I need to switch the existing CRUSH rules to only use the HDD device class first. Is there some way of doing this that doesn't result in 100% data movement? Simply replacing `step take default` with `step take default class hdd` for every CRUSH rule seems to completely shuffle the cluster data. I tried manually specifying the bucket IDs for the hdd hierarchy to at least be in the same order as the bucket IDs for the primary hierarchy, hoping having them sort the same would end up with the same data distribution, but that didn't work either. Is there some magic incantation to swap around the CRUSH rules/tree so that it results in exactly the same data distribution after adding the hdd class constraint? The set of potential OSDs should be identical (there are no SSDs yet), so the data movement seems to be some technicality of the CRUSH implementation... perhaps completely switching around the main id and hdd-class id of all the buckets would do it? (I'm a little afraid to mess with the main ids in a production cluster...). This cluster is already having I/O load issues (that's part of why I'm adding SSDs), so I'd really like to avoid a total data shuffle if possible. Thanks, - Hector