Aha, that's what I was looking for! And indeed, it seems to do exactly what I thought of doing, just move the bucket IDs. I mistakenly thought this functionality was for people who already had multiple parallel hierarchies in their crush tree, but it also works for a single default hierarchy. This did the trick: crushtool -i crush.old --reclassify --reclassify-root default hdd -o crush Thanks! On 2025/03/14 23:17, Eugen Block wrote: > The crushtool would do that with the --reclassify flag. There was a > thread here on this list a couple of months ago. I’m on my mobile, I > don’t have a link for you right now. But the docs should also contain > some examples, if I’m not mistaken. > > > Zitat von Hector Martin <marcan@xxxxxxxxx>: > >> 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 >> _______________________________________________ >> ceph-users mailing list -- ceph-users@xxxxxxx >> To unsubscribe send an email to ceph-users-leave@xxxxxxx > > > _______________________________________________ > ceph-users mailing list -- ceph-users@xxxxxxx > To unsubscribe send an email to ceph-users-leave@xxxxxxx - Hector _______________________________________________ ceph-users mailing list -- ceph-users@xxxxxxx To unsubscribe send an email to ceph-users-leave@xxxxxxx
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