Make parameter tunable

Signed-off-by: Paul Dagnelie <[email protected]>

Author: Paul Dagnelie

man/man4/zfs.4

@@ -615,6 +615,30 @@ redundancy.
 Defaults to 600 seconds and a value of zero disables disk sit-outs in general,
 including slow disk outlier detection.
 .
+.It Sy vdev_raidz_outlier_check_interval_ms Ns = Ns Sy 1000 Ns ms Po 1 sec Pc Pq ulong
+How often each RAID-Z and dRAID vdev will check for slow disk outliers.
+Increasing this interval will reduce the sensitivity of detection (since all
+I/Os since the last check are included in the statistics), but will slow the
+response to a disk developing a problem.
+Defaults to once per second; setting extremely small values may cause negative
+performance effects.
+.
+.It Sy vdev_raidz_outlier_insensitivity Ns = Ns Sy 50 Pq uint
+When performing slow outlier checks for RAID-Z and dRAID vdevs, this value is
+used to determine how far out an outlier must be before it counts as an event
+worth consdering.
+This is phrased as "insensitivity" because larger values result in fewer
+detections.
+Smaller values will result in more aggressive sitting out of disks that may have
+problems, but may significantly increase the rate of spurious sit-outs.
+.Pp
+To provide a more technical definition of this parameter, this is the multiple
+of the inter-quartile range (IQR) that is being used in a Tukey's Fence
+detection algorithm.
+This is much higher than a normal Tukey's Fence k-value, because the
+distribution under consideration is probably an extreme-value distribution,
+rather than a more typical Gaussian distribution.
+.
 .It Sy vdev_removal_max_span Ns = Ns Sy 32768 Ns B Po 32 KiB Pc Pq uint
 During top-level vdev removal, chunks of data are copied from the vdev
 which may include free space in order to trade bandwidth for IOPS.

module/zfs/vdev_raidz.c

@@ -5475,4 +5475,6 @@ ZFS_MODULE_PARAM(zfs_vdev, vdev_, read_sit_out_secs, ULONG, ZMOD_RW,
 	"Raidz/draid slow disk sit out time period in seconds");
 ZFS_MODULE_PARAM(zfs_vdev, vdev_, raidz_outlier_check_interval_ms, ULONG,
 	ZMOD_RW, "Interval to check for slow raidz/draid children");
+ZFS_MODULE_PARAM(zfs_vdev, vdev_, raidz_outlier_insensitivity, UINT,
+	ZMOD_RW, "How insensitive the slow raidz/draid child check should be");
 /* END CSTYLED */