Detect a slow raidz child during reads
A single slow responding disk can affect the overall read
performance of a raidz group. When a raidz child disk is
determined to be a persistent slow outlier, then have it
sit out during reads for a period of time. The raidz group
can use parity to reconstruct the data that was skipped.
Each time a slow disk is placed into a sit out period, its
vdev_stat.vs_slow_ios count is incremented and a zevent
class ereport.fs.zfs.delay is posted.
The length of the sit out period can be changed using the
raid_read_sit_out_secs module parameter. Setting it to
zero disables slow outlier detection.
Sponsored-by: Klara, Inc.
Sponsored-by: Wasabi Technology, Inc.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Paul Dagnelie <paul.dagnelie@klarasystems.com>
Contributions-by: Don Brady <don.brady@klarasystems.com>
Contributions-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #17227