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We are running on Hammer 0.94.7 and have had very bad experiences with PG folders splitting a sub-directory further. OSDs being marked out, hundreds of blocked requests, etc.
We have modified our settings and watched the behavior match the ceph documentation for splitting, but right now the subfolders are splitting outside of what the documentation says they should.
filestore_split_multiple * abs(filestore_merge_threshold) * 16 Our filestore_merge_threshold is set to 40. When we had our filestore_split_multiple set to 8, we were splitting subfolders when a subfolder had (8 * 40 * 16 = ) 5120 objects in the directory. In a different cluster we had to push that back again with elevated settings and the subfolders split when they had (16 * 40 * 16 = ) 10240 objects. We have another cluster that we're working with that is splitting at a value that seems to be a hardcoded maximum. The settings are (32 * 40 * 16 = ) 20480 objects before it should split, but it seems to be splitting subfolders at 12800 objects. Normally I would expect this number to be a power of 2, but we recently found another hardcoded maximum of the object map only allowing RBD's with a maximum 256,000,000 objects in them. The 12800 matches that as being a base 2 followed by a set of zero's to be the hardcoded maximum. Has anyone else encountered what seems to be a hardcoded maximum here? Are we missing a setting elsewhere that is capping us, or diminishing our value? Much more to the point, though, is there any way to mitigate how painful it is to split subfolders in PGs? So far it seems like the only way we can do it is to push up the setting to later drop it back down during a week that we plan to have our cluster plagued with blocked requests all while cranking our osd_heartbeat_grace so that we don't have flapping osds. A little more about our setup is that we have 32x 4TB HGST drives with 4x 200GB Intel DC3710 journals (8 drives per journal), dual hyper-threaded octa-core Xeon (32 virtual cores), 192GB memory, 10Gb redundant network... per storage node.
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