[LU-12909] DNE3: prefer local network MDT for mkdir()

• Type: Improvement
• Resolution: Unresolved
• Priority: Minor
• Assignee: WC Triage
• Reporter: Andreas Dilger

Description

As a further enhancement to the patch https://review.whamcloud.com/35825
"LU-12624 lod: alloc dir stripes by QoS" it would be useful to consider the "distance" between the client and the MDSes when choosing which MDT to create a directory on.

If there is an MDT is on the same LNet network as the client, then it should be preferred for mkdir over an MDT on a remote LNet network, unless it is very full. In most configurations, the MDTs are all the same "distance" from the client, but it would be useful to be able to prefer MDTs that are closer to get lower latency and better performance.

As an extension to this, the MDS should prefer allocating objects from OSTs that are on the same network as the client, as opposed to OSTs that are not on the client network.