In some common cases (when you have lots of objects per pg) ceph will warn about it.
2018-01-03 11:10 GMT+01:00 Marc Roos <m.r...@f1-outsourcing.eu>: > > > Is there a disadvantage to just always start pg_num and pgp_num with > something low like 8, and then later increase it when necessary? > > Question is then how to identify when necessary > > > > > > -----Original Message----- > From: Christian Wuerdig [mailto:christian.wuer...@gmail.com] > Sent: dinsdag 2 januari 2018 19:40 > To: 于相洋 > Cc: Ceph-User > Subject: Re: [ceph-users] Questions about pg num setting > > Have you had a look at http://ceph.com/pgcalc/? > > Generally if you have too many PGs per OSD you can get yourself into > trouble during recovery and backfilling operations consuming a lot more > RAM than you have and eventually making your cluster unusable (some more > info can be found here for example: > http://lists.ceph.com/pipermail/ceph-users-ceph.com/ > 2016-October/013614.html > but there are other threads on the ML). > Also currently you cannot reduce the number of PGs for a pool so you are > much better of starting with a lower value and then gradually increasing > it. > > The fact that the ceph developers introduced a config option which > prevents users from increasing the number of PGs if it exceeds the > configured limit should be a tell-tale sign that having too many PGs per > OSD is considered a problem (see also > https://bugzilla.redhat.com/show_bug.cgi?id=1489064 and linked PRs) > > On Wed, Dec 27, 2017 at 3:15 PM, 于相洋 <penglai...@gmail.com> wrote: > > Hi cephers, > > > > I have two questions about pg number setting. > > > > First : > > My storage informaiton is show as belows: > > HDD: 10 * 8TB > > CPU: Intel(R) Xeon(R) CPU E5645 @ 2.40GHz (24 cores) > > Memery: 64GB > > > > As my HDD capacity and my Mem is too large, so I want to set as many > > as 300 pgs to each OSD. Although 100 pgs per OSD is perferred. I want > > to know what is the disadvantage of setting too many pgs? > > > > > > Second: > > At begin ,I can not judge the capacity proportion of my workloads, so > > I can not set accurate pg numbers of different pools. How many pgs > > should I set for each pools first? > > -- > > To unsubscribe from this list: send the line "unsubscribe ceph-devel" > > in the body of a message to majord...@vger.kernel.org More majordomo > > info at http://vger.kernel.org/majordomo-info.html > _______________________________________________ > 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 > -- May the most significant bit of your life be positive.
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