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List:       ceph-users
Subject:    [ceph-users] Re: Not all OSDs in rack marked as down when the rack fails
From:       Wido den Hollander <wido () 42on ! com>
Date:       2020-10-30 10:28:06
Message-ID: 4161a02d-fb93-5884-a0a3-fdf94ec4462e () 42on ! com
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On 29/10/2020 18:58, Dan van der Ster wrote:
> Hi Wido,
> 
> Could it be one of these?
> 
> mon osd min up ratio
> mon osd min in ratio
> 
> 36/120 is 0.3 so it might be one of those magic ratios at play.

I thought of those settings and looked at it. The weird thing is that 
all 3 racks are equal and it works as expected in the other racks. There 
all 40 OSDs are marked as down properly.

These settings should also yield log messages in the MON's log, but they 
don't. Searching for 'ratio' in the logfile doesn't show me anything.

It's weird that osd.51 was only marked as down after 15 minutes because 
it didn't send a beacon to the MON. Other OSDs kept sending reports that 
it was down, but the MONs simply didn't act on it.

Wido

> 
> Cheers,
> 
> Dan
> 
> 
> On Thu, 29 Oct 2020, 18:05 Wido den Hollander, <wido@42on.com 
> <mailto:wido@42on.com>> wrote:
> 
>     Hi,
> 
>     I'm investigating an issue where 4 to 5 OSDs in a rack aren't marked as
>     down when the network is cut to that rack.
> 
>     Situation:
> 
>     - Nautilus cluster
>     - 3 racks
>     - 120 OSDs, 40 per rack
> 
>     We performed a test where we turned off the network Top-of-Rack for
>     each
>     rack. This worked as expected with two racks, but with the third
>     something weird happened.
> 
>       From the 40 OSDs which were supposed to be marked as down only 36
>     were
>     marked as down.
> 
>     In the end it took 15 minutes for all 40 OSDs to be marked as down.
> 
>     $ ceph config set mon mon_osd_reporter_subtree_level rack
> 
>     That setting is set to make sure that we only accept reports from other
>     racks.
> 
>     What we saw in the logs for example:
> 
>     2020-10-29T03:49:44.409-0400 7fbda185e700 10
>     mon.CEPH2-MON1-206-U39@0(leader).osd e107102  osd.51 has 54 reporters,
>     239.856038 grace (20.000000 + 219.856 + 7.43801e-23), max_failed_since
>     2020-10-29T03:47:22.374857-0400
> 
>     But osd.51 was still not marked as down after 54 reporters have
>     reported
>     that it is actually down.
> 
>     I checked, no ping or other traffic possible to osd.51. Host is
>     unreachable.
> 
>     Another osd was marked as down, but it took a couple of minutes as well:
> 
>     2020-10-29T03:50:54.455-0400 7fbda185e700 10
>     mon.CEPH2-MON1-206-U39@0(leader).osd e107102  osd.37 has 48 reporters,
>     221.378970 grace (20.000000 + 201.379 + 6.34437e-23), max_failed_since
>     2020-10-29T03:47:12.761584-0400
>     2020-10-29T03:50:54.455-0400 7fbda185e700  1
>     mon.CEPH2-MON1-206-U39@0(leader).osd e107102  we have enough reporters
>     to mark osd.37 down
> 
>     In the end osd.51 was marked as down, but only after the MON decided to
>     do so:
> 
>     2020-10-29T03:53:44.631-0400 7fbda185e700  0 log_channel(cluster) log
>     [INF] : osd.51 marked down after no beacon for 903.943390 seconds
>     2020-10-29T03:53:44.631-0400 7fbda185e700 -1
>     mon.CEPH2-MON1-206-U39@0(leader).osd e107104 no beacon from osd.51
>     since
>     2020-10-29T03:38:40.689062-0400, 903.943390 seconds ago.  marking down
> 
>     I haven't seen this happen before in any cluster. It's also strange
>     that
>     this only happens in this rack, the other two racks work fine.
> 
>     ID    CLASS  WEIGHT      TYPE NAME
>         -1         1545.35999  root default
> 
>     -206          515.12000      rack 206
> 
>         -7           27.94499          host CEPH2-206-U16
>     ...
>     -207          515.12000      rack 207
> 
>        -17           27.94499          host CEPH2-207-U16
>     ...
>     -208          515.12000      rack 208
> 
>        -31           27.94499          host CEPH2-208-U16
>     ...
> 
>     That's how the CRUSHMap looks like. Straight forward and 3x replication
>     over 3 racks.
> 
>     This issue only occurs in rack *207*.
> 
>     Has anybody seen this before or knows where to start?
> 
>     Wido
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