multipathd treats "stand-by" path as active(ghost) and reinstate path.This
causes I/O hang issues and lots of "change" udev events in cases where only
stand-by paths are present in multipath map and target supports only
implicit
tpgs mode(active/passive arrays)
This can happen during system boot where only stand-by paths are discovered
first and continuous retry of I/O's by dm-multipath and change(failed)
events
are hogging multipathd and slowing down the entire boot process with large
number of volumes mapped (~100s).
Selecting path checkers other than tur is not a solution as well, as they
will
continuously throw messages saying paths are failed for stand-by state.
This patch will prevent re-instate of stand-by paths in this situation and
thus prevent unnecessary i/o with failed events during boot or when active
array goes down temporarily.
Detailed steps to hit the I/O hang issue even with no_path_retry:
devices {
device {
vendor "Nimble"
product "Server"
path_grouping_policy group_by_prio
detect_prio yes
hardware_handler "1 alua"
path_checker tur
failback immediate
fast_io_fail_tmo 10
no_path_retry 30
path_selector "round-robin 0"
}
}
1. Delete all active paths.
mpathal (2e0176ad6309077166c9ce90033bfa248_1) dm-2 Nimble,Server
size=20G features='1 queue_if_no_path' hwhandler='1 alua' wp=rw
`-+- policy='round-robin 0' prio=1 status=active
|- 8:0:5:1 sdg 8:96 active ghost running
`- 8:0:6:1 sdh 8:112 active ghost running
2. Issue I/O on mpath with zero active paths.
dd if=/dev/mapper/mpathal of=/dev/null bs=512 count=1 iflag=direct &
Nov 23 15:10:36 hitdev-rhel67 multipathd: mpathal: sdg - tur checker
reports path is in standby state
Nov 23 15:10:36 hitdev-rhel67 multipathd: 8:96: reinstated
Nov 23 15:10:36 hitdev-rhel67 multipathd: mpathal: queue_if_no_path enabled
Nov 23 15:10:36 hitdev-rhel67 multipathd: mpathal: Recovered to normal mode
Nov 23 15:10:36 hitdev-rhel67 multipathd: mpathal: remaining active paths:
1
Nov 23 15:10:36 hitdev-rhel67 kernel: sd 8:0:5:1: alua: port group 02
state S non-preferred supports tolusna
Nov 23 15:10:36 hitdev-rhel67 kernel: device-mapper: multipath: Failing
path 8:96.
Nov 23 15:10:36 hitdev-rhel67 multipathd: 8:96: mark as failed
Nov 23 15:10:36 hitdev-rhel67 multipathd: mpathal: Entering recovery mode:
max_retries=20
Nov 23 15:10:36 hitdev-rhel67 multipathd: mpathal: remaining active paths:
0
3. Monitor udev events every 5 seconds.
# udevadm monitor
monitor will print the received events for:
UDEV - the event which udev sends out after rule processing
KERNEL - the kernel uevent
KERNEL[1448320131.061837] change /devices/virtual/block/dm-2 (block)
KERNEL[1448320131.064802] change /devices/virtual/block/dm-2 (block)
UDEV [1448320131.082838] change /devices/virtual/block/dm-2 (block)
UDEV [1448320131.102134] change /devices/virtual/block/dm-2 (block)
KERNEL[1448320135.551737] change /devices/virtual/block/dm-2 (block)
KERNEL[1448320135.552701] change /devices/virtual/block/dm-2 (block)
UDEV [1448320135.571634] change /devices/virtual/block/dm-2 (block)
UDEV [1448320135.591017] change /devices/virtual/block/dm-2 (block)
KERNEL[1448320136.553368] change /devices/virtual/block/dm-2 (block)
KERNEL[1448320136.554298] change /devices/virtual/block/dm-2 (block)
UDEV [1448320136.572733] change /devices/virtual/block/dm-2 (block)
UDEV [1448320136.592089] change /devices/virtual/block/dm-2 (block)
KERNEL[1448320140.555389] change /devices/virtual/block/dm-2 (block)
KERNEL[1448320140.556369] change /devices/virtual/block/dm-2 (block)
UDEV [1448320140.574944] change /devices/virtual/block/dm-2 (block)
UDEV [1448320140.594076] change /devices/virtual/block/dm-2 (block)
Signed-off-by: ShivaKrishna Merla <shiva.krishna@xxxxxxxxxxxxxxxxx>
---
libmultipath/propsel.c | 2 +-
libmultipath/structs.h | 1 +
multipathd/main.c | 21 ++++++++++++++++-----
3 files changed, 18 insertions(+), 6 deletions(-)
diff --git a/libmultipath/propsel.c b/libmultipath/propsel.c
index f64d5e4..b9e389f 100644
--- a/libmultipath/propsel.c
+++ b/libmultipath/propsel.c
@@ -374,7 +374,7 @@ detect_prio(struct path * pp)
int ret;
struct prio *p = &pp->prio;
- if (get_target_port_group_support(pp->fd) <= 0)
+ if ((pp->tpgs = get_target_port_group_support(pp->fd)) <= 0)
return;
ret = get_target_port_group(pp->fd);
if (ret < 0)
diff --git a/libmultipath/structs.h b/libmultipath/structs.h
index 5f68a8e..ef5fb7e 100644
--- a/libmultipath/structs.h
+++ b/libmultipath/structs.h
@@ -193,6 +193,7 @@ struct path {
int detect_prio;
int watch_checks;
int wait_checks;
+ int tpgs;
char * uid_attribute;
char * getuid;
struct prio prio;
diff --git a/multipathd/main.c b/multipathd/main.c
index bf3423f..7faa4bd 100644
--- a/multipathd/main.c
+++ b/multipathd/main.c
@@ -62,6 +62,7 @@ static int use_watchdog;
#include <pgpolicies.h>
#include <uevent.h>
#include <log.h>
+#include "prioritizers/alua_rtpg.h"
#include "main.h"
#include "pidfile.h"
@@ -1299,11 +1300,21 @@ check_path (struct vectors * vecs, struct path *
pp)
pp->watch_checks--;
add_active = 0;
}
- if (reinstate_path(pp, add_active)) {
- condlog(3, "%s: reload map", pp->dev);
- ev_add_path(pp, vecs);
- pp->tick = 1;
- return 0;
+
+ /*
+ * don't reinstate failed path, if its in stand-by
+ * and if target supports only implicit tpgs mode.
+ * this will prevent unnecessary i/o by dm on stand-by
+ * paths if there are no other active paths in map.
+ */
+ if (newstate != PATH_GHOST || pp->mpp->nr_active > 0 ||
+ pp->tpgs != TPGS_IMPLICIT) {
+ if (reinstate_path(pp, add_active)) {
+ condlog(3, "%s: reload map", pp->dev);
+ ev_add_path(pp, vecs);
+ pp->tick = 1;
+ return 0;
+ }
}
new_path_up = 1;
--
--
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