[LU-19424] show/set LMV MDT mkdir starting index

• Type: Improvement
• Resolution: Fixed
• Priority: Medium
• Fix Version/s: Lustre 2.17.0
• Affects Version/s: Lustre 2.14.0, Lustre 2.17.0
• Severity: 3
• Assignee: Andreas Dilger
• Reporter: Andreas Dilger

Description

Expose the lmv_qos_rr_index variable that controls which MDT index to start round-robin subdirectory creation to userspace with a new lmv.*.qos_rr_start_index parameter.

The client-selected qos_rr_start_index is based on the hash of the client's first NID, and is intended to allow a distributed mechanism to avoid many clients starting subdirectory creation on the first MDT in a round-robin directory-per-(client,rank) creation scenario.

The new parameter will allow debugging whether these values are being set properly at startup (i.e. uniformly distributed across MDTs), or if some centralized mechanism is needed to initiliaze this value (e.g. sequence counter on MDT0000 that is returned to the client in obd_connect_data or similar).

Issue Links

• is related to: LU-18891 increase default DNE MDT "lfs setdirstripe --max-inherit-rr"
• is related to: LU-19540 assign client mountpoints a unique "start index" for load distribution