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Understanding/Using Pools

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Hmm... When I do the following:

cp crush-original-decompiled crush-original-decompiled-edited
nano crush-original-decompiled-edited # remove unsed rules
crushtool -c crush-original-decompiled-edited -o crush-original-decompiled-edited.bin # compile rule
crushtool -i crush-original-decompiled-edited.bin --reclassify --reclassify-root default hdd -o  crush-new.bin # modify crushmap und change default class to hdd
crushtool -i  crush-original --compare crush-new.bin # compare old and new crushmap

I get:

rule 0 had 0/10240 mismatched mappings (0)
rule 1 had 18432/18432 mismatched mappings (1)
rule 2 had 18432/18432 mismatched mappings (1)
rule 3 had 0/10240 mismatched mappings (0)
rule 4 had 10240/10240 mismatched mappings (1)
warning: maps are NOT equivalent

That seems to me that I will face a lot of data movement. Right? I would get the same (I think) when I just change the rule for the pool like this:

ceph osd pool set ceph-replicated-3 crush_rule by-host-hhd

as stated earlier, i understand you have only 1 current pool that uses default rule and wanted to change it to an hdd specific rule so you can add ssd pools afterwards.

if so then, as stated, remove the unused class specific rules you added before running the tool, and compare the tool output with the edited input not with the original one that had unused rules.

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