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Hi list,
I am testing cache tier in writeback mode by rados bench.
The test resutl is confusing.The write performance is worse than without a cache tier. For my understanding the pool with cache tier in writeback mode should performace like all ssd pool(client get ack after data write to hot storage) if the cache dosen't need to be flushed.
But in my wirte test,the pool with cache tier has poorer performance than even all hdd pool.
And I inspect the pool stat to find out that there is only 244 objects in the hot-pool and 695 objects in the cold pool(the write test wrote 695 objects).But for my setting 695 objects shouldn't trigger the flush.
Is there any setting or concept I wrongly understood ? my cache tier setting: # ceph osd tier add cold-pool hot-pool
pool 'hot-pool' is now (or already was) a tier of 'cold-pool'
#
# ceph osd tier cache-mode hot-pool writeback
set cache-mode for pool 'hot-pool' to writeback
#
# ceph osd tier set-overlay cold-pool hot-pool
overlay for 'cold-pool' is now (or already was) 'hot-pool'
#
# ceph osd pool set hot-pool hit_set_type bloom
set pool 39 hit_set_type to bloom
#
# ceph osd pool set hot-pool hit_set_count 10
set pool 39 hit_set_count to 10
#
# ceph osd pool set hot-pool hit_set_period 3600
set pool 39 hit_set_period to 3600
#
# ceph osd pool set hot-pool target_max_bytes 2400000000000
set pool 39 target_max_bytes to 2400000000000
#
# ceph osd pool set hot-pool target_max_objects 300000
set pool 39 target_max_objects to 300000
#
# ceph osd pool set hot-pool cache_target_dirty_ratio 0.4
set pool 39 cache_target_dirty_ratio to 0.4
#
# ceph osd pool set hot-pool cache_target_dirty_high_ratio 0.6
set pool 39 cache_target_dirty_high_ratio to 0.6
#
# ceph osd pool set hot-pool cache_target_full_ratio 0.8
set pool 39 cache_target_full_ratio to 0.8
#
# ceph osd pool set hot-pool cache_min_flush_age 600
set pool 39 cache_min_flush_age to 600
#
# ceph osd pool set hot-pool cache_min_evict_age 1800
set pool 39 cache_min_evict_age to 1800
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