Thank you so much, Dan!
Can you confirm for me that for pool7, which has 2048/2048 for pg_num and 883/2048 for pgp_num, we should change pg_num or pgp_num? And can they be different for a single pool, or does pg_num and pgp_num have to always be the same?
IF we just set pgp_num to 890 we will have pg_num at 2048 and pgp_num at 890, is that ok? Because if we reduce the pg_num by 1200 it will just start a whole new load of misplaced object rebalancing. Won't it?
Thank you,
Ray
-----Original Message-----
From: Dan van der Ster <dvanders@xxxxxxxxx>
Sent: Wednesday, April 13, 2022 11:11 AM
To: Ray Cunningham <ray.cunningham@xxxxxxxxxxxxxx>
Cc: ceph-users@xxxxxxx
Subject: Re: Stop Rebalancing
Hi, Thanks.
norebalance/nobackfill are useful to pause ongoing backfilling, but aren't the best option now to get the PGs to go active+clean and let the mon db come back under control. Unset those before continuing.
I think you need to set the pg_num for pool1 to something close to but less than 926. (Or whatever the pg_num_target is when you run the command below).
The idea is to let a few more merges complete successfully but then once all PGs are active+clean to take a decision about the other interventions you want to carry out.
So this ought to be good:
ceph osd pool set pool1 pg_num 920
Then for pool7 this looks like splitting is ongoing. You should be able to pause that by setting the pg_num to something just above 883.
I would do:
ceph osd pool set pool7 pg_num 890
It may even be fastest to just set those pg_num values to exactly what the current pgp_num_target is. You can try it.
Once your cluster is stable again, then you should set those to the nearest power of two.
Personally I would wait for #53729 to be fixed before embarking on future pg_num changes.
(You'll have to mute a warning in the meantime -- check the docs after the warning appears).
Cheers, dan
On Wed, Apr 13, 2022 at 5:16 PM Ray Cunningham <ray.cunningham@xxxxxxxxxxxxxx> wrote:
>
> Perfect timing, I was just about to reply. We have disabled autoscaler on all pools now.
>
> Unfortunately, I can't just copy and paste from this system...
>
> `ceph osd pool ls detail` only 2 pools have any difference.
> pool1: pgnum 940, pgnum target 256, pgpnum 926 pgpnum target 256
> pool7: pgnum 2048, pgnum target 2048, pgpnum883, pgpnum target 2048
>
> ` ceph osd pool autoscale-status`
> Size is defined
> target size is empty
> Rate is 7 for all pools except pool7, which is 1.3333333730697632 Raw
> capacity is defined Ratio for pool1 is .0177, pool7 is .4200 and all
> others is 0 Target and Effective Ratio is empty Bias is 1.0 for all
> PG_NUM: pool1 is 256, pool7 is 2048 and all others are 32.
> New PG_NUM is empty
> Autoscale is now off for all
> Profile is scale-up
>
>
> We have set norebalance and nobackfill and are watching to see what happens.
>
> Thank you,
> Ray
>
> -----Original Message-----
> From: Dan van der Ster <dvanders@xxxxxxxxx>
> Sent: Wednesday, April 13, 2022 10:00 AM
> To: Ray Cunningham <ray.cunningham@xxxxxxxxxxxxxx>
> Cc: ceph-users@xxxxxxx
> Subject: Re: Stop Rebalancing
>
> One more thing, could you please also share the `ceph osd pool autoscale-status` ?
>
>
> On Tue, Apr 12, 2022 at 9:50 PM Ray Cunningham <ray.cunningham@xxxxxxxxxxxxxx> wrote:
> >
> > Thank you Dan! I will definitely disable autoscaler on the rest of our pools. I can't get the PG numbers today, but I will try to get them tomorrow. We definitely want to get this under control.
> >
> > Thank you,
> > Ray
> >
> >
> > -----Original Message-----
> > From: Dan van der Ster <dvanders@xxxxxxxxx>
> > Sent: Tuesday, April 12, 2022 2:46 PM
> > To: Ray Cunningham <ray.cunningham@xxxxxxxxxxxxxx>
> > Cc: ceph-users@xxxxxxx
> > Subject: Re: Stop Rebalancing
> >
> > Hi Ray,
> >
> > Disabling the autoscaler on all pools is probably a good idea. At least until https://tracker.ceph.com/issues/53729 is fixed. (You are likely not susceptible to that -- but better safe than sorry).
> >
> > To pause the ongoing PG merges, you can indeed set the pg_num to the current value. This will allow the ongoing merge complete and prevent further merges from starting.
> > From `ceph osd pool ls detail` you'll see pg_num, pgp_num, pg_num_target, pgp_num_target... If you share the current values of those we can help advise what you need to set the pg_num to to effectively pause things where they are.
> >
> > BTW -- I'm going to create a request in the tracker that we improve the pg autoscaler heuristic. IMHO the autoscaler should estimate the time to carry out a split/merge operation and avoid taking one-way decisions without permission from the administrator. The autoscaler is meant to be helpful, not degrade a cluster for 100 days!
> >
> > Cheers, Dan
> >
> >
> >
> > On Tue, Apr 12, 2022 at 9:04 PM Ray Cunningham <ray.cunningham@xxxxxxxxxxxxxx> wrote:
> > >
> > > Hi Everyone,
> > >
> > > We just upgraded our 640 OSD cluster to Ceph 16.2.7 and the resulting rebalancing of misplaced objects is overwhelming the cluster and impacting MON DB compaction, deep scrub repairs and us upgrading legacy bluestore OSDs. We have to pause the rebalancing if misplaced objects or we're going to fall over.
> > >
> > > Autoscaler-status tells us that we are reducing our PGs by 700'ish which will take us over 100 days to complete at our current recovery speed. We disabled autoscaler on our biggest pool, but I'm concerned that it's already on the path to the lower PG count and won't stop adding to our misplaced count after drop below 5%. What can we do to stop the cluster from finding more misplaced objects to rebalance? Should we set the PG num manually to what our current count is? Or will that cause even more havoc?
> > >
> > > Any other thoughts or ideas? My goals are to stop the rebalancing temporarily so we can deep scrub and repair inconsistencies, upgrade legacy bluestore OSDs and compact our MON DBs (supposedly MON DBs don't compact when you aren't 100% active+clean).
> > >
> > > Thank you,
> > > Ray
> > >
> > > _______________________________________________
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> > > email to ceph-users-leave@xxxxxxx
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