On 6/24/21 5:34 PM, Frank Schilder wrote:
Please, in such situations where developers seem to have to make a definite choice, consider the possibility of offering operators to choose the alternative that suits their use case best. Adding further options seems far better than limiting functionality in a way that becomes a terrible burden in certain, if not many use cases.
Yeah, I agree.
In ceph fs there have been many such decisions that allow for different answers from a user/operator perspective. For example, I would prefer if I could get rid of the attempted higher POSIX compliance level of ceph fs compared with Lustre, just disable all the client-caps and cache-coherence management and turn it into an awesome scale-out parallel file system. The attempt of POSIX compliant handling of simultaneous writes to files offers nothing to us, but costs huge in performance and forces users to move away from perfectly reasonable HPC work flows. Also, that it takes a TTL to expire before changes on one client become visible on another (unless direct_io is used for all IO) is perfectly acceptable for us given the potential performance gain due to simpler client-MDS communication.
Isn't that where LazyIO is for? See https://docs.ceph.com/en/latest/cephfs/lazyio/
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