I created radosgw pools.
secondaryzone.rgw.buckets.data pool is
configured as EC 8+2 (jerasure).
Did you override the default bluestore_min_alloc_size_hdd (64k in that
version IIRC) when creating your hdd OSDs? If not, all of the small objects
produced by that EC configuration will be leading to significant on-disk
allocation overhead.
Josh