An alternative to user5994461's suggestion would be to switch from CephFS to a different distributed filesystem. If you need POSIX and can't go directly to S3 you could try ObjectiveFS[1]. Using local SSD instance store and memory for caching you can get very good performance even for small file workloads[2].
[1]: https://objectivefs.com [2]: https://objectivefs.com/howto/performance-amazon-efs-vs-obje...