[LU-12273] DNE3: Metadata overstriping

• Type: New Feature
• Resolution: Fixed
• Priority: Minor
• Fix Version/s: Lustre 2.16.0
• Labels: IO500 dne3
• Assignee: Patrick Farrell
• Reporter: Patrick Farrell (Inactive)

Description

LU-9846 describes the overstriping feature for data, which allows placing > 1 stripe per OST.  This can be done with MDTs as well, for somewhat similar reasons:

"it allows more concurrency on the MDT, exceeding single-directory size limitations, directory migration/compaction, etc." (per Andreas)

This exists in limited form today, accessible with a fail loc:
OBD_FAIL_LARGE_STRIPE (0x1703)

Which is used in sanity test 300k to put a bunch of stripes on MDT0:

        #define OBD_FAIL_LARGE_STRIPE   0x1703
        $LCTL set_param fail_loc=0x1703
        $LFS setdirstripe -i 0 -c192 $DIR/$tdir/striped_dir ||
                error "set striped dir err

Actually doing this as a feature requires various other enabling changes, but this test shows it should be possible.  It's also possible to use the method in this test to create temporary setups for benchmarking this idea to confirm it's worth pursuing.

Issue Links

• is related to: LU-12926 lfs mkdir -c can cause repeated MDT indexes
• is related to: LU-18244 add 'lfs mkdir -C -N' overstriping support
• is related to: LU-17756 tunable limit for MDT overstripe factor
• is related to: LU-9846 Overstriping - more than stripe per OST per component