> 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 <dvanders@xxxxxxxxx> 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 <frans@xxxxxx> 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 <dvanders@xxxxxxxxx>
> > Sent: 29 August 2022 19:13
> > To: Frank Schilder
> > Subject: Re: 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 <frans@xxxxxx<mailto:frans@xxxxxx>> 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 <dvanders@xxxxxxxxx<mailto:dvanders@xxxxxxxxx>>
> > Sent: 29 August 2022 16:52:52
> > To: Frank Schilder
> > Cc: ceph-users@xxxxxxx<mailto:ceph-users@xxxxxxx>
> > Subject: Re: 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 <frans@xxxxxx<mailto:frans@xxxxxx>> 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@xxxxxxx<mailto:ceph-users@xxxxxxx>
> > > To unsubscribe send an email to ceph-users-leave@xxxxxxx<mailto:ceph-users-leave@xxxxxxx>
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