> Note: "step chose" was selected by creating the crush rule with ceph on pool
> creation. If the default should be "step choseleaf" (with OSD buckets), then
> the automatic crush rule generation in ceph ought to be fixed for EC profiles.
Interesting. Which exact command was used to create the pool?
> These experiments indicate that there is a very weird behaviour implemented,
> I would actually call this a serious bug.
I don't think this is a bug. Each of your attempts with different
_tries values changed the max iterations of the various loops in
crush. Since this takes crush on different "paths" to find a valid
OSD, the output is going to be different.
> The resulting mapping should be independent of the maximum number of trials
No this is wrong.. the "tunables" change the mapping. The important
thing is that every node + client in the cluster agrees on the mapping
-- and indeed since they all use the same tunables, including the
values for *_tries, they will all agree on the up/acting set.
Cheers, Dan
On Tue, Aug 30, 2022 at 1:10 PM Frank Schilder <fr...@dtu.dk> wrote:
>
> Hi Dan,
>
> thanks a lot for looking into this. I can't entirely reproduce your results.
> Maybe we are using different versions and there was a change? I'm testing
> with the octopus 16.2.16 image: quay.io/ceph/ceph:v15.2.16.
>
> Note: "step chose" was selected by creating the crush rule with ceph on pool
> creation. If the default should be "step choseleaf" (with OSD buckets), then
> the automatic crush rule generation in ceph ought to be fixed for EC profiles.
>
> My results with the same experiments as you did, I can partly confirm and
> partly I see oddness that I would consider a bug (reported at the very end):
>
> rule fs-data {
> id 1
> type erasure
> min_size 3
> max_size 6
> step take default
> step choose indep 0 type osd
> step emit
> }
>
> # osdmaptool --test-map-pg 4.1c osdmap.bin
> osdmaptool: osdmap file 'osdmap.bin'
> parsed '4.1c' -> 4.1c
> 4.1c raw ([6,1,4,5,3,2147483647], p6) up ([6,1,4,5,3,2147483647], p6) acting
> ([6,1,4,5,3,1], p6)
>
> rule fs-data {
> id 1
> type erasure
> min_size 3
> max_size 6
> step take default
> step chooseleaf indep 0 type osd
> step emit
> }
>
> # osdmaptool --test-map-pg 4.1c osdmap.bin
> osdmaptool: osdmap file 'osdmap.bin'
> parsed '4.1c' -> 4.1c
> 4.1c raw ([6,1,4,5,3,2], p6) up ([6,1,4,5,3,2], p6) acting ([6,1,4,5,3,1], p6)
>
> So far, so good. Now the oddness:
>
> rule fs-data {
> id 1
> type erasure
> min_size 3
> max_size 6
> step set_chooseleaf_tries 5
> step set_choose_tries 100
> step take default
> step chooseleaf indep 0 type osd
> step emit
> }
>
> # osdmaptool --test-map-pg 4.1c osdmap.bin
> osdmaptool: osdmap file 'osdmap.bin'
> parsed '4.1c' -> 4.1c
> 4.1c raw ([6,1,4,5,3,8], p6) up ([6,1,4,5,3,8], p6) acting ([6,1,4,5,3,1], p6)
>
> How can this be different?? I thought crush returns on the first successful
> mapping. This ought to be identical to the previous one. It gets even more
> weird:
>
> rule fs-data {
> id 1
> type erasure
> min_size 3
> max_size 6
> step set_chooseleaf_tries 50
> step set_choose_tries 200
> step take default
> step chooseleaf indep 0 type osd
> step emit
> }
>
> # osdmaptool --test-map-pg 4.1c osdmap.bin
> osdmaptool: osdmap file 'osdmap.bin'
> parsed '4.1c' -> 4.1c
> 4.1c raw ([6,1,4,5,3,7], p6) up ([6,1,4,5,3,2147483647], p6) acting
> ([6,1,4,5,3,1], p6)
>
> Whaaaaat???? We increase the maximum number of trials for searching and we
> end up with an invalid mapping??
>
> These experiments indicate that there is a very weird behaviour implemented,
> I would actually call this a serious bug. The resulting mapping should be
> independent of the maximum number of trials (if I understood the crush
> algorithm correctly). In any case, a valid mapping should never be replaced
> in favour of an invalid one (containing a down+out OSD).
>
> For now there is a happy end on my test cluster:
>
> # ceph pg dump pgs_brief | grep 4.1c
> dumped pgs_brief
> 4.1c active+remapped+backfilling [6,1,4,5,3,8] 6
> [6,1,4,5,3,1] 6
>
> Please look into the extremely odd behaviour reported above. I'm quite
> confident that this is unintended if not dangerous behaviour and should be
> corrected. I'm willing to file a tracker item with the data above. I'm
> actually wondering if this might be related to
> https://tracker.ceph.com/issues/56995 .
>
> Thanks for tracking this down and best regards,
> =================
> Frank Schilder
> AIT Risø Campus
> Bygning 109, rum S14
>
> ________________________________________
> From: Dan van der Ster <dvand...@gmail.com>
> Sent: 30 August 2022 12:16:37
> To: Frank Schilder
> Cc: ceph-users@ceph.io
> Subject: Re: [ceph-users] Bug in crush algorithm? 1 PG with the same OSD
> twice.
>
> BTW, the defaults for _tries seems to work too:
>
>
> # diff -u crush.txt crush.txt2
> --- crush.txt 2022-08-30 11:27:41.941836374 +0200
> +++ crush.txt2 2022-08-30 11:55:45.601891010 +0200
> @@ -90,10 +90,10 @@
> type erasure
> min_size 3
> max_size 6
> - step set_chooseleaf_tries 50
> - step set_choose_tries 200
> + step set_chooseleaf_tries 5
> + step set_choose_tries 100
> step take default
> - step choose indep 0 type osd
> + step chooseleaf indep 0 type osd
> step emit
> }
>
> # osdmaptool --test-map-pg 4.1c osdmap.bin2
> osdmaptool: osdmap file 'osdmap.bin2'
> parsed '4.1c' -> 4.1c
> 4.1c raw ([6,1,4,5,3,8], p6) up ([6,1,4,5,3,8], p6) acting ([6,1,4,5,3,1], p6)
>
>
> -- dan
>
> On Tue, Aug 30, 2022 at 11:50 AM Dan van der Ster <dvand...@gmail.com> wrote:
> >
> > BTW, I vaguely recalled seeing this before. Yup, found it:
> > https://tracker.ceph.com/issues/55169
> >
> > On Tue, Aug 30, 2022 at 11:46 AM Dan van der Ster <dvand...@gmail.com>
> > wrote:
> > >
> > > > 2. osd.7 is destroyed but still "up" in the osdmap.
> > >
> > > Oops, you can ignore this point -- this was an observation I had while
> > > playing with the osdmap -- your osdmap.bin has osd.7 down correctly.
> > >
> > > In case you're curious, here was what confused me:
> > >
> > > # osdmaptool osdmap.bin2 --mark-up-in --mark-out 7 --dump plain
> > > osd.7 up out weight 0 up_from 3846 up_thru 3853 down_at 3855
> > > last_clean_interval [0,0)
> > > [v2:10.41.24.15:6810/1915819,v1:10.41.24.15:6811/1915819]
> > > [v2:192.168.0.15:6808/1915819,v1:192.168.0.15:6809/1915819]
> > > destroyed,exists,up
> > >
> > > Just ignore this ...
> > >
> > >
> > >
> > > -- dan
> > >
> > > On Tue, Aug 30, 2022 at 11:41 AM Dan van der Ster <dvand...@gmail.com>
> > > wrote:
> > > >
> > > > Hi Frank,
> > > >
> > > > I suspect this is a combination of issues.
> > > > 1. You have "choose" instead of "chooseleaf" in rule 1.
> > > > 2. osd.7 is destroyed but still "up" in the osdmap.
> > > > 3. The _tries settings in rule 1 are not helping.
> > > >
> > > > Here are my tests:
> > > >
> > > > # osdmaptool --test-map-pg 4.1c osdmap.bin
> > > > osdmaptool: osdmap file 'osdmap.bin'
> > > > parsed '4.1c' -> 4.1c
> > > > 4.1c raw ([6,1,4,5,3,2147483647], p6) up ([6,1,4,5,3,2147483647], p6)
> > > > acting ([6,1,4,5,3,1], p6)
> > > >
> > > > ^^ This is what you observe now.
> > > >
> > > > # diff -u crush.txt crush.txt2
> > > > --- crush.txt 2022-08-30 11:27:41.941836374 +0200
> > > > +++ crush.txt2 2022-08-30 11:31:29.631491424 +0200
> > > > @@ -93,7 +93,7 @@
> > > > step set_chooseleaf_tries 50
> > > > step set_choose_tries 200
> > > > step take default
> > > > - step choose indep 0 type osd
> > > > + step chooseleaf indep 0 type osd
> > > > step emit
> > > > }
> > > > # crushtool -c crush.txt2 -o crush.map2
> > > > # cp osdmap.bin osdmap.bin2
> > > > # osdmaptool --import-crush crush.map2 osdmap.bin2
> > > > osdmaptool: osdmap file 'osdmap.bin2'
> > > > osdmaptool: imported 1166 byte crush map from crush.map2
> > > > osdmaptool: writing epoch 4990 to osdmap.bin2
> > > > # osdmaptool --test-map-pg 4.1c osdmap.bin2
> > > > osdmaptool: osdmap file 'osdmap.bin2'
> > > > parsed '4.1c' -> 4.1c
> > > > 4.1c raw ([6,1,4,5,3,7], p6) up ([6,1,4,5,3,2147483647], p6) acting
> > > > ([6,1,4,5,3,1], p6)
> > > >
> > > > ^^ The mapping is now "correct" in that it doesn't duplicate the
> > > > mapping to osd.1. However it tries to use osd.7 which is destroyed but
> > > > up.
> > > >
> > > > You might be able to fix that by fully marking osd.7 out.
> > > > I can also get a good mapping by removing the *_tries settings from
> > > > rule 1:
> > > >
> > > > # diff -u crush.txt crush.txt2
> > > > --- crush.txt 2022-08-30 11:27:41.941836374 +0200
> > > > +++ crush.txt2 2022-08-30 11:38:14.068102835 +0200
> > > > @@ -90,10 +90,8 @@
> > > > type erasure
> > > > min_size 3
> > > > max_size 6
> > > > - step set_chooseleaf_tries 50
> > > > - step set_choose_tries 200
> > > > step take default
> > > > - step choose indep 0 type osd
> > > > + step chooseleaf indep 0 type osd
> > > > step emit
> > > > }
> > > > ...
> > > > # osdmaptool --test-map-pg 4.1c osdmap.bin2
> > > > osdmaptool: osdmap file 'osdmap.bin2'
> > > > parsed '4.1c' -> 4.1c
> > > > 4.1c raw ([6,1,4,5,3,2], p6) up ([6,1,4,5,3,2], p6) acting
> > > > ([6,1,4,5,3,1], p6)
> > > >
> > > > Note that I didn't need to adjust the reweights:
> > > >
> > > > # osdmaptool osdmap.bin2 --tree
> > > > osdmaptool: osdmap file 'osdmap.bin2'
> > > > ID CLASS WEIGHT TYPE NAME STATUS REWEIGHT PRI-AFF
> > > > -1 2.44798 root default
> > > > -7 0.81599 host tceph-01
> > > > 0 hdd 0.27199 osd.0 up 0.87999 1.00000
> > > > 3 hdd 0.27199 osd.3 up 0.98000 1.00000
> > > > 6 hdd 0.27199 osd.6 up 0.92999 1.00000
> > > > -3 0.81599 host tceph-02
> > > > 2 hdd 0.27199 osd.2 up 0.95999 1.00000
> > > > 4 hdd 0.27199 osd.4 up 0.89999 1.00000
> > > > 8 hdd 0.27199 osd.8 up 0.89999 1.00000
> > > > -5 0.81599 host tceph-03
> > > > 1 hdd 0.27199 osd.1 up 0.89999 1.00000
> > > > 5 hdd 0.27199 osd.5 up 1.00000 1.00000
> > > > 7 hdd 0.27199 osd.7 destroyed 0 1.00000
> > > >
> > > >
> > > > Does this work in real life?
> > > >
> > > > Cheers, Dan
> > > >
> > > >
> > > > On Mon, Aug 29, 2022 at 7:38 PM Frank Schilder <fr...@dtu.dk> wrote:
> > > > >
> > > > > Hi Dan,
> > > > >
> > > > > please find attached (only 7K, so I hope it goes through).
> > > > > md5sum=1504652f1b95802a9f2fe3725bf1336e
> > > > >
> > > > > I was playing a bit around with the crush map and found out the
> > > > > following:
> > > > >
> > > > > 1) Setting all re-weights to 1 does produce valid mappings. However,
> > > > > it will lead to large imbalances and is impractical in operations.
> > > > >
> > > > > 2) Doing something as simple/stupid as the following also results in
> > > > > valid mappings without having to change the weights:
> > > > >
> > > > > rule fs-data {
> > > > > id 1
> > > > > type erasure
> > > > > min_size 3
> > > > > max_size 6
> > > > > step set_chooseleaf_tries 50
> > > > > step set_choose_tries 200
> > > > > step take default
> > > > > step chooseleaf indep 3 type host
> > > > > step emit
> > > > > step take default
> > > > > step chooseleaf indep -3 type host
> > > > > step emit
> > > > > }
> > > > >
> > > > > rule fs-data {
> > > > > id 1
> > > > > type erasure
> > > > > min_size 3
> > > > > max_size 6
> > > > > step set_chooseleaf_tries 50
> > > > > step set_choose_tries 200
> > > > > step take default
> > > > > step choose indep 3 type osd
> > > > > step emit
> > > > > step take default
> > > > > step choose indep -3 type osd
> > > > > step emit
> > > > > }
> > > > >
> > > > > Of course, now the current weights are probably unsuitable as
> > > > > everything moves around. Its probably also a lot more total tries to
> > > > > get rid of mappings with duplicate OSDs.
> > > > >
> > > > > I probably have to read the code to understand how drawing straws
> > > > > from 8 different buckets with non-zero probabilities can lead to an
> > > > > infinite sequence of failed attempts of getting 6 different ones.
> > > > > There seems to be a hard-coded tunable that turns seemingly infinite
> > > > > into finite somehow.
> > > > >
> > > > > The first modified rule will probably lead to better distribution of
> > > > > load, but bad distribution of data if a disk goes down (considering
> > > > > the tiny host- and disk numbers). The second rule seems to be almost
> > > > > as good or bad as the default one (step choose indep 0 type osd),
> > > > > except that it does produce valid mappings where the default rule
> > > > > fails.
> > > > >
> > > > > I will wait with changing the rule in the hope that you find a more
> > > > > elegant solution to this riddle.
> > > > >
> > > > > Best regards,
> > > > > =================
> > > > > Frank Schilder
> > > > > AIT Risø Campus
> > > > > Bygning 109, rum S14
> > > > >
> > > > > ________________________________________
> > > > > From: Dan van der Ster <dvand...@gmail.com>
> > > > > Sent: 29 August 2022 19:13
> > > > > To: Frank Schilder
> > > > > Subject: Re: [ceph-users] Bug in crush algorithm? 1 PG with the same
> > > > > OSD twice.
> > > > >
> > > > > Hi Frank,
> > > > >
> > > > > Could you share the osdmap so I can try to solve this riddle?
> > > > >
> > > > > Cheers , Dan
> > > > >
> > > > >
> > > > > On Mon, Aug 29, 2022, 17:26 Frank Schilder
> > > > > <fr...@dtu.dk<mailto:fr...@dtu.dk>> wrote:
> > > > > Hi Dan,
> > > > >
> > > > > thanks for your answer. I'm not really convinced that we hit a corner
> > > > > case here and even if its one, it seems quite relevant for production
> > > > > clusters. The usual way to get a valid mapping is to increase the
> > > > > number of tries. I increased the following max trial numbers, which I
> > > > > would expect to produce a mapping for all PGs:
> > > > >
> > > > > # diff map-now.txt map-new.txt
> > > > > 4c4
> > > > > < tunable choose_total_tries 50
> > > > > ---
> > > > > > tunable choose_total_tries 250
> > > > > 93,94c93,94
> > > > > < step set_chooseleaf_tries 5
> > > > > < step set_choose_tries 100
> > > > > ---
> > > > > > step set_chooseleaf_tries 50
> > > > > > step set_choose_tries 200
> > > > >
> > > > > When I test the map with crushtool it does not report bad mappings.
> > > > > Am I looking at the wrong tunables to increase? It should be possible
> > > > > to get valid mappings without having to modify the re-weights.
> > > > >
> > > > > Thanks again for your help!
> > > > > =================
> > > > > Frank Schilder
> > > > > AIT Risø Campus
> > > > > Bygning 109, rum S14
> > > > >
> > > > > ________________________________________
> > > > > From: Dan van der Ster <dvand...@gmail.com<mailto:dvand...@gmail.com>>
> > > > > Sent: 29 August 2022 16:52:52
> > > > > To: Frank Schilder
> > > > > Cc: ceph-users@ceph.io<mailto:ceph-users@ceph.io>
> > > > > Subject: Re: [ceph-users] Bug in crush algorithm? 1 PG with the same
> > > > > OSD twice.
> > > > >
> > > > > Hi Frank,
> > > > >
> > > > > CRUSH can only find 5 OSDs, given your current tree, rule, and
> > > > > reweights. This is why there is a NONE in the UP set for shard 6.
> > > > > But in ACTING we see that it is refusing to remove shard 6 from osd.1
> > > > > -- that is the only copy of that shard, so in this case it's helping
> > > > > you rather than deleting the shard altogether.
> > > > > ACTING == what the OSDs are serving now.
> > > > > UP == where CRUSH wants to place the shards.
> > > > >
> > > > > I suspect that this is a case of CRUSH tunables + your reweights
> > > > > putting CRUSH in a corner case of not finding 6 OSDs for that
> > > > > particular PG.
> > > > > If you set the reweights all back to 1, it probably finds 6 OSDs?
> > > > >
> > > > > Cheers, Dan
> > > > >
> > > > >
> > > > > On Mon, Aug 29, 2022 at 4:44 PM Frank Schilder
> > > > > <fr...@dtu.dk<mailto:fr...@dtu.dk>> wrote:
> > > > > >
> > > > > > Hi all,
> > > > > >
> > > > > > I'm investigating a problem with a degenerated PG on an octopus
> > > > > > 15.2.16 test cluster. It has 3Hosts x 3OSDs and a 4+2 EC pool with
> > > > > > failure domain OSD. After simulating a disk fail by removing an OSD
> > > > > > and letting the cluster recover (all under load), I end up with a
> > > > > > PG with the same OSD allocated twice:
> > > > > >
> > > > > > PG 4.1c, UP: [6,1,4,5,3,NONE] ACTING: [6,1,4,5,3,1]
> > > > > >
> > > > > > OSD 1 is allocated twice. How is this even possible?
> > > > > >
> > > > > > Here the OSD tree:
> > > > > >
> > > > > > ID CLASS WEIGHT TYPE NAME STATUS REWEIGHT PRI-AFF
> > > > > > -1 2.44798 root default
> > > > > > -7 0.81599 host tceph-01
> > > > > > 0 hdd 0.27199 osd.0 up 0.87999 1.00000
> > > > > > 3 hdd 0.27199 osd.3 up 0.98000 1.00000
> > > > > > 6 hdd 0.27199 osd.6 up 0.92999 1.00000
> > > > > > -3 0.81599 host tceph-02
> > > > > > 2 hdd 0.27199 osd.2 up 0.95999 1.00000
> > > > > > 4 hdd 0.27199 osd.4 up 0.89999 1.00000
> > > > > > 8 hdd 0.27199 osd.8 up 0.89999 1.00000
> > > > > > -5 0.81599 host tceph-03
> > > > > > 1 hdd 0.27199 osd.1 up 0.89999 1.00000
> > > > > > 5 hdd 0.27199 osd.5 up 1.00000 1.00000
> > > > > > 7 hdd 0.27199 osd.7 destroyed 0 1.00000
> > > > > >
> > > > > > I tried already to change some tunables thinking about
> > > > > > https://docs.ceph.com/en/octopus/rados/troubleshooting/troubleshooting-pg/#crush-gives-up-too-soon,
> > > > > > but giving up too soon is obviously not the problem. It is
> > > > > > accepting a wrong mapping.
> > > > > >
> > > > > > Is there a way out of this? Clearly this is calling for trouble if
> > > > > > not data loss and should not happen at all.
> > > > > >
> > > > > > Best regards,
> > > > > > =================
> > > > > > Frank Schilder
> > > > > > AIT Risø Campus
> > > > > > Bygning 109, rum S14
> > > > > > _______________________________________________
> > > > > > ceph-users mailing list --
> > > > > > ceph-users@ceph.io<mailto:ceph-users@ceph.io>
> > > > > > To unsubscribe send an email to
> > > > > > ceph-users-le...@ceph.io<mailto:ceph-users-le...@ceph.io>
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