diff options
| author | Serapheim Dimitropoulos <[email protected]> | 2019-06-06 13:08:41 -0700 |
|---|---|---|
| committer | Brian Behlendorf <[email protected]> | 2019-06-06 13:08:41 -0700 |
| commit | cb020f0d86f6a1902f49c6e7d1f934850188acc2 (patch) | |
| tree | 1537cedbae662465bd6d798e31e26e7bab39c930 /man | |
| parent | 627f5117a3ec4b435e6ee85026a1da671de44c7b (diff) | |
Reduced IOPS when all vdevs are in the zfs_mg_fragmentation_threshold
Historically while doing performance testing we've noticed that IOPS
can be significantly reduced when all vdevs in the pool are hitting
the zfs_mg_fragmentation_threshold percentage. Specifically in a
hypothetical pool with two vdevs, what can happen is the following:
Vdev A would go above that threshold and only vdev B would be used.
Then vdev B would pass that threshold but vdev A would go below it
(we've been freeing from A to allocate to B). The allocations would
go back and forth utilizing one vdev at a time with IOPS taking a hit.
Empirically, we've seen that our vdev selection for allocations is
good enough that fragmentation increases uniformly across all vdevs
the majority of the time. Thus we set the threshold percentage high
enough to avoid hitting the speed bump on pools that are being pushed
to the edge. We effectively disable its effect in the majority of the
cases but we don't remove (at least for now) just in case we hit any
weird behavior in the future.
Reviewed-by: George Melikov <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Reviewed-by: Matt Ahrens <[email protected]>
Signed-off-by: Serapheim Dimitropoulos <[email protected]>
Closes #8859
Diffstat (limited to 'man')
| -rw-r--r-- | man/man5/zfs-module-parameters.5 | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/man/man5/zfs-module-parameters.5 b/man/man5/zfs-module-parameters.5 index 5bca12e06..282563f13 100644 --- a/man/man5/zfs-module-parameters.5 +++ b/man/man5/zfs-module-parameters.5 @@ -1817,7 +1817,7 @@ this value. If a metaslab group exceeds this threshold then it will be skipped unless all metaslab groups within the metaslab class have also crossed this threshold. .sp -Default value: \fB85\fR. +Default value: \fB95\fR. .RE .sp |