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.wuerdig@xxxxxxxxx] Sent: dinsdag 2 januari 2018 19:40 To: 于相洋 Cc: Ceph-User Subject: Re: 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 <penglaiyxy@xxxxxxxxx> 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 majordomo@xxxxxxxxxxxxxxx More majordomo > info at http://vger.kernel.org/majordomo-info.html _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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