Regarding on the cache tiering performance topic discussed on yesterday's meeting:
- Need to test performance with commit to avoid promotion on first read:
Zhiqiang actually did some tests based on https://github.com/ceph/ceph/commit/0ed3adc1e0a74bf9548d1d956aece11f019afee0 .
We actually observed with Promote on 2nd read, we can get up to 2x IOPS improvement, (although still far below expectation), and 66% improvement on latency on the following test configuration.
2 OSD nodes with 10G Nic, each with 8x 1T HDD and 6x 400G DC3700 SSD, 2 SSDs used for Journal, while 4 SSD used for cache tiering.
* Cache Tiering Setting:
Cache size: 1000G (target_max_bytes: 1000000000000); Dirty ratio: 20% (cache_target_dirty_ratio: 0.2); Full ratio: 20% (cache_target_full_ratio: 0.2)
Fio 4K random Read/write/Mixed tests.
Without cache tiering, the performance for 4K random read is: 1021, with latency ~3000ms (QD=256).
With cache tiering, the performance for 4K random read is: 359, with latency ~6000ms.
With cache tiering + promote on second read, 4K random read performance is: ~800, with latency ~1500ms.
We can share the data either during CDS https://wiki.ceph.com/Planning/Blueprints/Hammer/osd%3A_tiering%3A_fine-grained_promotion_unit or next weekly performance meeting.
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