Hi Everyone, Getting close to cracking my understanding of cache tiering, and ec pools. Stuck on one anomaly which I do not understand — spent hours reviewing docs online, can’t seem to pin point what I’m doing wrong. Referencing http://ceph.com/docs/master/rados/operations/cache-tiering/ <http://ceph.com/docs/master/rados/operations/cache-tiering/>
Setup: Test / PoC Lab environment (not production) 1x [26x OSD/MON host] 1x MON VM Erasure coded pool consisting of 10 spinning OSDs (journals on SSDs - 5:1 spinner:SSD ratio) Cache tier consisting of 2 SSD OSDs Issue: Cache tier is not honoring configured thresholds. In my particular case, I have 2 OSDs in pool ‘cache’ (140G each == 280G total pool capacity). Pool cache is configured with replica factor of 2 (size = 2, min size = 1) Initially I tried the following settings: ceph osd pool set cache cache_target_dirty_ratio 0.3 ceph osd pool set cache cache_target_full_ratio 0.7 ceph osd pool set cache cache_min_flush_age 1 ceph osd pool set cache cache_min_evict_age 1 My cache tier’s utilization hit 96%+, causing the pool to run out of capacity. I realized that in a replicated pool, only 1/2 the capacity is available and made the following adjustments: ceph osd pool set cache cache_target_dirty_ratio 0.1 ceph osd pool set cache cache_target_full_ratio 0.3 ceph osd pool set cache cache_min_flush_age 1 ceph osd pool set cache cache_min_evict_age 1 The above implies that 0.3 = 60% of replicated (2x) pool size) and 0.1 = 20% of replicated (2x) pool size. Even with above revised values, I still see the cache tier getting full. The cache tier can only be flushed / evicted by manually running the following: rados -p cache cache-flush-evict-all Thank you.
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