Mastering Ceph - Second Edition

Tuning CephFS

There are two main performance characteristics that determine CephFS performance—the speed of metadata access and the speed of data access, although in the majority of cases, both of these contribute to access requests.

It is important to understand that in CephFS, once the metadata has been retrieved for a file, reads to the actual file data do not require any further metadata operations until the file is closed by the client. Similarly, when writing files, only when dirty data is flushed by the client is the metadata updated. Thus, for a large, sequential buffered IO, metadata operations will likely only make up a small proportion of the total cluster IO.

Similarly, for CephFS filesystems that are dealing with a large number ...