Feature #3462
openclient: Add null-io debug options to client for testing
0%
Description
When testing metadata behavior and performance (interaction between mds and client), in most cases we don't care about the data, and can avoid the overhead of writing/reading the data to the osds (or caching it at the client).
This is a proposal to add two options to the ceph config:
The first: client null io = true would skip sending I/O requests to the osds from the client (Client doesn't invoke filer->write_trunc and ObjecterWriteback doesn't invoke objecter->write_trunc), instead just completes the I/O request as if the request had been sent.
The second, client null data = true bypasses the client cache entirely (skips the objectcacher->file_write in Client::_write).
An alternative to using config options could be to define a path (/.ceph_null_io/) that would do the above whenever any file rooted at that path was accessed. This would allow us to test metadata behavior and performance on deployments without twiddling the config.