Reef release candidate - v18.1.2

Hi everyone, This is the second release candidate for Reef. The Reef release comes with a new RockDB version (7.9.2) [0], which incorporates several performance improvements and features. Our internal testing doesn't show any side effects from the new version, but we are very eager to hear community feedback on it. This is the first release to have the ability to tune RockDB settings per column family [1], which allows for more granular tunings to be applied to different kinds of data stored in RocksDB. A new set of settings has been used in Reef to optimize performance for most kinds of workloads with a slight penalty in some cases, outweighed by large improvements in use cases such as RGW, in terms of compactions and write amplification. We would highly encourage community members to give these a try against their performance benchmarks and use cases. The detailed list of changes in terms of RockDB and BlueStore can be found in https://pad.ceph.com/p/reef-rc-relnotes. If any of our community members would like to help us with performance investigations or regression testing of the Reef release candidate, please feel free to provide feedback via email or in https://pad.ceph.com/p/reef_scale_testing. For more active discussions, please use the #ceph-at-scale slack channel in ceph-storage.slack.com. This RC has gone thru partial testing due to issues we are experiencing in the sepia lab. Please try it out and report any issues you encounter. Happy testing! Thanks, YuriW