[LU-13287] DNE2 - Shared directory performance does not scale and starts to plateau beyond 2MDTs

• Type: Improvement
• Resolution: Not a Bug
• Priority: Major
• Affects Version/s: Lustre 2.13.0
• Labels: dne2 llnl performance
• Assignee: WC Triage
• Reporter: Petros Koutoupis

Description

While testing in an environment with a single parent directory following by 1 shared sub directory for all client mdtest ranks, we are observe very little scaling when moving to more than 2 MDTs. See below for 1 million objects per MDT, 0K File Creates:

1 MDTs - 83,948
2 MDTs - 115,929
3 MDTs - 123,186
4 MDTs - 130,846

Stats and deletes are showcasing similar results. It seems to not follow a linear scale but instead plateaus. It would also seem that we are not the only ones to observe this. A recent Cambridge University IO-500 presentation presented a slide with very similar results (fourth from the bottom): https://www.eofs.eu/_media/events/lad19/03_matt_raso-barnett-io500-cambridge.pdf

Issue Links

• is related to: LU-9436 DNE2 - performance improvement with wide stripping directory