On Thu, Sep 13, 2018 at 3:05 PM, Graham Allan <g...@umn.edu> wrote:
> I'm now following up to my earlier message regarding data migration from old
> to new hardware in our ceph cluster. As part of this we wanted to move to
> device-class-based crush rules. For the replicated pools the directions for
> this were straightforward; for our EC pool, it wasn't so clear, but I
> proceeded via the outline below: defining a new EC profile and associated
> crush rule, then finally, last Wednesday (5 Sept) updating the crush rule
> for the pool.
>
> Data migration started well for the first 36 or so hours, then the storage
> backend became very unstable with OSDs dropping out and failing to peer...
> capped off by the mons running out of disk space. After correcting the mon
> disk issue, stability seemed to be restored by dropping down max backfills
> and a few other parameters, eg
>
> osd max backfills = 4
> osd recovery max active = 1
> osd max recovery threads = 1
>
> I also had to stop then restart all OSDs to stop the peering storm, but the
> data migration has been proceeding fine since then.
>
> However I do see transfer errors fetching some files out of radosgw - the
> transfer just hangs then aborts. I'd guess this probably due to one pg stuck
> down, due to a lost (failed HDD) osd. I think there is no alternative to
> declare the osd lost, but I wish I understood better the implications of the
> "recovery_state" and "past_intervals" output by ceph pg query:
> https://pastebin.com/8WrYLwVt
What are you curious about here? The past intervals is listing the
OSDs which were involved in the PG since it was last clean, then each
acting set and the intervals it was active for.
>
> I find it disturbing/odd that the acting set of osds lists only 3/6
> available; implies that without getting one of these back it would be
> impossible to recover the data (from 4+2 EC). However the dead osd 98 only
> appears in the most recent (?) interval - presumably during the flapping
> period, during which time client writes were unlikely (radosgw disabled).
>
> So if 98 were marked lost would it roll back to the prior interval? I am not
> certain how to interpret this information!
Yes, that’s what should happen if it’s all as you outline here.
It *is* quite curious that the PG apparently went active with only 4
members in a 4+2 system — it's supposed to require at least k+1 (here,
5) by default. Did you override the min_size or something?
-Greg
>
> Running luminous 12.2.7 if it makes a difference.
>
> Thanks as always for pointers,
>
> Graham
>
> On 07/18/2018 02:35 PM, Graham Allan wrote:
>>
>> Like many, we have a typical double root crush map, for hdd vs ssd-based
>> pools. We've been running luminous for some time, so in preparation for a
>> migration to new storage hardware, I wanted to migrate our pools to use the
>> new device-class based rules; this way I shouldn't need to perpetuate the
>> double hdd/ssd crush map for new hardware...
>>
>> I understand how to migrate our replicated pools, by creating new
>> replicated crush rules, and migrating them one at a time, but I'm confused
>> on how to do this for erasure pools.
>>
>> I can create a new class-aware EC profile something like:
>>
>>> ceph osd erasure-code-profile set ecprofile42_hdd k=4 m=2
>>> crush-device-class=hdd crush-failure-domain=host
>>
>>
>> then a new crush rule from this:
>>
>>> ceph osd crush rule create-erasure ec42_hdd ecprofile42_hdd
>>
>>
>> So mostly I want to confirm that is is safe to change the crush rule for
>> the EC pool. It seems to make sense, but then, as I understand it, you can't
>> change the erasure code profile for a pool after creation; but this seems to
>> implicitly do so...
>>
>> old rule:
>>>
>>> rule .rgw.buckets.ec42 {
>>> id 17
>>> type erasure
>>> min_size 3
>>> max_size 20
>>> step set_chooseleaf_tries 5
>>> step take platter
>>> step chooseleaf indep 0 type host
>>> step emit
>>> }
>>
>>
>> old ec profile:
>>>
>>> # ceph osd erasure-code-profile get ecprofile42
>>> crush-failure-domain=host
>>> directory=/usr/lib/x86_64-linux-gnu/ceph/erasure-code
>>> k=4
>>> m=2
>>> plugin=jerasure
>>> technique=reed_sol_van
>>
>>
>> new rule:
>>>
>>> rule ec42_hdd {
>>> id 7
>>> type erasure
>>> min_size 3
>>> max_size 6
>>> step set_chooseleaf_tries 5
>>> step set_choose_tries 100
>>> step take default class hdd
>>> step chooseleaf indep 0 type host
>>> step emit
>>> }
>>
>>
>> new ec profile:
>>>
>>> # ceph osd erasure-code-profile get ecprofile42_hdd
>>> crush-device-class=hdd
>>> crush-failure-domain=host
>>> crush-root=default
>>> jerasure-per-chunk-alignment=false
>>> k=4
>>> m=2
>>> plugin=jerasure
>>> technique=reed_sol_van
>>> w=8
>>
>>
>> These are both ec42 but I'm not sure why the old rule has "max size 20"
>> (perhaps because it was generated a long time ago under hammer?).
>>
>> Thanks for any feedback,
>>
>> Graham
>
>
> --
> Graham Allan
> Minnesota Supercomputing Institute - g...@umn.edu
>
>
> _______________________________________________
> ceph-users mailing list
> ceph-users@lists.ceph.com
> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
_______________________________________________
ceph-users mailing list
ceph-users@lists.ceph.com
http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
