[dm-devel] [PATCH 2/2] multipath.conf.5: Improve checker_timeout description

[Benjamin Marzinski]

I was asked to explain how checker_timeout works for checkers like
directio, that don't issue scsi commands with an explicit timeout.
Also, undeprecate the directio checker.

Signed-off-by: Benjamin Marzinski <bmarzins at redhat.com>
---
 multipath/multipath.conf.5 | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/multipath/multipath.conf.5 b/multipath/multipath.conf.5
index ea66a01e..8ef3a747 100644
--- a/multipath/multipath.conf.5
+++ b/multipath/multipath.conf.5
@@ -472,8 +472,12 @@ The default is: \fB<unset>\fR
 .
 .TP
 .B path_checker
-The default method used to determine the paths state. Possible values
-are:
+The default method used to determine the path's state. The synchronous
+checkers (all except \fItur\fR and \fIdirectio\fR) will cause multipathd to
+pause most activity, waiting up to \fIchecker_timeout\fR seconds for the path
+to respond. The asynchronous checkers (\fItur\fR and \fIdirectio\fR) will not
+pause multipathd. Instead, multipathd will check for a response once per
+second, until \fIchecker_timeout\fR seconds have elapsed. Possible values are:
 .RS
 .TP 12
 .I readsector0
@@ -499,10 +503,8 @@ Check the path state for LSI/Engenio/NetApp RDAC class as NetApp SANtricity E/EF
 Series, and OEM arrays from IBM DELL SGI STK and SUN.
 .TP
 .I directio
-(Deprecated) Read the first sector with direct I/O. If you have a large number
-of paths, or many AIO users on a system, you may need to use sysctl to
-increase fs.aio-max-nr. This checker is being deprecated, it could cause
-spurious path failures under high load. Please use \fItur\fR instead.
+Read the first sector with direct I/O. This checker could cause spurious path
+failures under high load. Increasing \fIchecker_timeout\fR can help with this.
 .TP
 .I cciss_tur
 (Hardware-dependent)
@@ -639,8 +641,10 @@ The default is: \fBno\fR
 .
 .TP
 .B checker_timeout
-Specify the timeout to use for path checkers and prioritizers that issue SCSI
-commands with an explicit timeout, in seconds.
+Specify the timeout to use for path checkers and prioritizers, in seconds.
+Only prioritizers that issue scsi commands use checker_timeout.  If a path
+does not respond to the checker command after \fIchecker_timeout\fR
+seconds have elapsed, it is considered down.
 .RS
 .TP
 The default is: in \fB/sys/block/sd<x>/device/timeout\fR
-- 
2.17.2