[ClusterLabs] Antw: [EXT] Re: Q: sbd: Which parameter controls "error: servant_md: slot read failed in servant."?

Thu Feb 17 04:49:27 EST 2022

On Thu, Feb 17, 2022 at 10:14 AM Ulrich Windl <
Ulrich.Windl at rz.uni-regensburg.de> wrote:

> >>> Klaus Wenninger <kwenning at redhat.com> schrieb am 16.02.2022 um 16:59
> in
> Nachricht
> <CALrDAo0Lm9ue9p2L_Q=8oJ9_9r0ejEvXrUm8DUKL5q8D9yQy2w at mail.gmail.com>:
> > On Wed, Feb 16, 2022 at 4:26 PM Klaus Wenninger <kwenning at redhat.com>
> wrote:
> >
> >>
> >>
> >> On Wed, Feb 16, 2022 at 3:09 PM Ulrich Windl <
> >> Ulrich.Windl at rz.uni-regensburg.de> wrote:
> >>
> >>> Hi!
> >>>
> >>> When changing some FC cables I noticed that sbd complained 2 seconds
> >>> after the connection went down (event though the device is multi-pathed
> >>> with other paths being still up).
> >>> I don't know any sbd parameter being set so low that after 2 seconds
> sbd
> >>> would panic. Which parameter (if any) is responsible for that?
> >>>
> >>> In fact multipath takes up to 5 seconds to adjust paths.
> >>>
> >>> Here are some sample events (sbd-1.5.0+20210720.f4ca41f-3.6.1.x86_64
> from
> >>> SLES15 SP3):
> >>> Feb 14 13:01:36 h18 kernel: qla2xxx [0000:41:00.0]-500b:3: LOOP DOWN
> >>> detected (2 7 0 0).
> >>> Feb 14 13:01:38 h18 sbd[6621]: /dev/disk/by-id/dm-name-SBD_1-3P2:
> >>> error: servant_md: slot read failed in servant.
> >>> Feb 14 13:01:38 h18 sbd[6619]: /dev/disk/by-id/dm-name-SBD_1-3P1:
> >>> error: servant_md: mbox read failed in servant.
> >>> Feb 14 13:01:40 h18 sbd[6615]:  warning: inquisitor_child: Servant
> >>> /dev/disk/by-id/dm-name-SBD_1-3P1 is outdated (age: 11)
> >>> Feb 14 13:01:40 h18 sbd[6615]:  warning: inquisitor_child: Servant
> >>> /dev/disk/by-id/dm-name-SBD_1-3P2 is outdated (age: 11)
> >>> Feb 14 13:01:40 h18 sbd[6615]:  warning: inquisitor_child: Majority of
> >>> devices lost - surviving on pacemaker
> >>> Feb 14 13:01:42 h18 kernel: sd 3:0:3:2: rejecting I/O to offline device
> >>> Feb 14 13:01:42 h18 kernel: blk_update_request: I/O error, dev sdbt,
> >>> sector 2048 op 0x0:(READ) flags 0x4200 phys_seg 1 prio class 1
> >>> Feb 14 13:01:42 h18 kernel: device-mapper: multipath: 254:17: Failing
> >>> path 68:112.
> >>> Feb 14 13:01:42 h18 kernel: sd 3:0:1:2: rejecting I/O to offline device
> >>>
> >> Sry forgotten to address the following.
> >
> > Guess your sbd-package predates
> >
> https://github.com/ClusterLabs/sbd/commit/9e6cbbad9e259de374cbf41b713419c342
> > 528db1
> > and thus doesn't properly destroy the io-context using the aio-api.
> > This flaw has been in kind of since ever and I actually found it due to a
> > kernel-issue that made
> > all block-io done the way sbd is doing it (aio + O_SYNC + O_DIRECT
> Actually
> > never successfully
> > tracked it down to the real kernel issue playing with kprobes. But it was
> > gone on the next kernel
> > update
> > ) timeout.
> > Without survival on pacemaker it would have suicided after
> > msgwait-timeout (10s in your case probably).
> > Would be interesting what happens if you raise msgwait-timeout to a value
> > that would allow
> > another read attempt.
> > Does your setup actually recover? Could be possible that it doesn't
> missing
> > the fix referenced above.
>
> For completeness: Yes, sbd did recover:
> Feb 14 13:01:42 h18 sbd[6615]:  warning: cleanup_servant_by_pid: Servant
> for /dev/disk/by-id/dm-name-SBD_1-3P1 (pid: 6619) has terminated
> Feb 14 13:01:42 h18 sbd[6615]:  warning: cleanup_servant_by_pid: Servant
> for /dev/disk/by-id/dm-name-SBD_1-3P2 (pid: 6621) has terminated
> Feb 14 13:01:42 h18 sbd[31668]: /dev/disk/by-id/dm-name-SBD_1-3P1:
>  notice: servant_md: Monitoring slot 4 on disk
> /dev/disk/by-id/dm-name-SBD_1-3P1
> Feb 14 13:01:42 h18 sbd[31669]: /dev/disk/by-id/dm-name-SBD_1-3P2:
>  notice: servant_md: Monitoring slot 4 on disk
> /dev/disk/by-id/dm-name-SBD_1-3P2
> Feb 14 13:01:49 h18 sbd[6615]:   notice: inquisitor_child: Servant
> /dev/disk/by-id/dm-name-SBD_1-3P1 is healthy (age: 0)
> Feb 14 13:01:49 h18 sbd[6615]:   notice: inquisitor_child: Servant
> /dev/disk/by-id/dm-name-SBD_1-3P2 is healthy (age: 0)
>

Good to see that!
Did you try several times?
I have some memory that when testing with the kernel mentioned before
behavior
changed after a couple of timeouts and it wasn't able to create the
read-request
anymore (without the fix mentioned) - assume some kind of resource depletion
due to previously hanging attempts not destroyed properly.
But that behavior might heavily depend on the kernel-version and as your
attempts
do terminate with failure in the kernel some time later that might resolve
issues
as well (in my case they would like hang forever from kernel pov).
As you seem to have sbd rebuilt anyway for your timer-checks ... would be
interesting if with the fix the delayed timeout-messages from the kernel
would
disappear.

Regards,
Klaus

>
> Feb 14 13:02:10 h18 kernel: qla2xxx [0000:41:00.0]-500a:3: LOOP UP
> detected (8 Gbps).
> Feb 14 13:02:15 h18 multipathd[5180]: SBD_1-3P1: remaining active paths: 3
> Feb 14 13:02:15 h18 multipathd[5180]: SBD_1-3P1: sdbl - tur checker
> reports path is up
> Feb 14 13:02:15 h18 multipathd[5180]: SBD_1-3P1: remaining active paths: 4
> Feb 14 13:02:16 h18 multipathd[5180]: SBD_1-3P2: sdbu - tur checker
> reports path is up
> Feb 14 13:02:16 h18 multipathd[5180]: SBD_1-3P2: remaining active paths: 3
> Feb 14 13:02:16 h18 multipathd[5180]: SBD_1-3P2: sdbo - tur checker
> reports path is up
> Feb 14 13:02:16 h18 multipathd[5180]: SBD_1-3P2: remaining active paths: 4
>
> >
> > Regards,
> > Klaus
> >
> >>
> >>> Most puzzling is the fact that sbd reports a problem 4 seconds before
> the
> >>> kernel reports an I/O error. I guess sbd "times out" the pending read.
> >>>
> >> Yep - that is timeout_io defaulting to 3s.
> >> You can set it with -I daemon start parameter.
> >> Together with the rest of the default-timeout-scheme the 3s do make
> sense.
> >> Not sure but if you increase that significantly you might have to adapt
> >> other timeouts.
> >> There are a certain number of checks regarding relationship of timeouts
> >> but they might not be exhaustive.
> >>
> >>>
> >>> The thing is: Both SBD disks are on different storage systems, each
> being
> >>> connected by two separate FC fabrics, but still when disconnecting one
> >>> cable from the host sbd panics.
> >>> My guess is if "surviving on pacemaker" would not have happened, the
> node
> >>> would be fenced; is that right?
> >>>
> >>> The other thing I wonder is the "outdated age":
> >>> How can the age be 11 (seconds) when the disk was disconnected 4
> seconds
> >>> ago?
> >>> It seems here the age is "current time - time_of_last read" instead of
> >>> "current_time - time_when read_attempt_started".
> >>>
> >> Exactly! And that is the correct way to do it as we need to record the
> >> time passed since last successful read.
> >> There is no value in starting the clock when we start the read attempt
> as
> >> these attempts are not synced throughout
> >> the cluster.
> >>
> >> Regards,
> >> Klaus
> >>
> >>>
> >>> Regards,
> >>> Ulrich
> >>>
> >>>
> >>>
> >>>
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