[LU-10777] DoM performance is bad with FIO write

• Type: Technical task
• Resolution: Fixed
• Priority: Major
• Fix Version/s: Lustre 2.13.0, Lustre 2.12.3
• Labels: DoM2 ORNL
• Assignee: Mikhail Pershin
• Reporter: Mikhail Pershin

Description

FIO test does a lot more RPCs to the MDT with DOM files comparing with OSTs files:

DOM files:
WRITE: BW 5900KiB/sec, IOPS 737, lat (7/83624/83631)usec
----- MDC RPCs: 118696
----- OSC RPCs: 252

OST files:
WRITE: BW 9738KiB/sec, IOPS 1217, lat (5/47728/47734)usec
----- MDC RPCs: 49668
----- OSC RPCs: 12302

so there are about 12K IO-related RPCs to the OST and about 70K extra RPCs to the MDT in the same test. That looks like OST writes are cached much better with FIO write pattern than writes to MDT.