Hi, huge, deadly, IO :-) Imagine, everything has to multiplied 1 time. Thats nothing what will go smooth :-) -- Mit freundlichen Gruessen / Best regards Oliver Dzombic IP-Interactive mailto:info@xxxxxxxxxxxxxxxxx Anschrift: IP Interactive UG ( haftungsbeschraenkt ) Zum Sonnenberg 1-3 63571 Gelnhausen HRB 93402 beim Amtsgericht Hanau Geschäftsführung: Oliver Dzombic Steuer Nr.: 35 236 3622 1 UST ID: DE274086107 Am 06.04.2016 um 16:41 schrieb dan@xxxxxxxxxxxxxxxxx: > Will changing the replication size from 2 to 3 cause huge I/O resources > to be used, or does this happen quietly in the background? > > > On 2016-04-06 00:40, Christian Balzer wrote: >> Hello, >> >> Brian already mentioned a number very pertinent things, I've got a few >> more: >> >> On Tue, 05 Apr 2016 10:48:49 -0400 dan@xxxxxxxxxxxxxxxxx wrote: >> >>> In a 12 OSD setup, the following config is there: >>> >>> (OSDs * 100) >>> Total PGs = ---------- >>> pool size >>> >> >> The PGcalc page at http://ceph.com/pgcalc/ is quite helpful and >> contains a >> lot of background info as well. >> >> As Brian said, you can never decrease PG count, but growing it is also a >> very I/O intensive operation and you want to avoid that as much as >> possible. >> >>> >>> So with 12 OSD's and a pool size of 2 replicas, this would equal Total >>> PGs of 600 as per this url: >> PGcalc with a target of 200 PGs per OSD (doubling of cluster size >> expected) gives us 1024, which is also what I would go for myself. >> >> However if this a production cluster and your OSDs are NOT RAID1 or very >> very reliable, fast and well monitored SSDs you're basically asking >> Murphy >> to come visit, destroying your data while eating babies and washing them >> down with bath water. >> >> The default replication size was changed to 3 for a very good reason, >> there are plenty of threads in this ML about failure scenarios and >> probabilities. >> >> Christian >> >>> >>> http://docs.ceph.com/docs/master/rados/operations/placement-groups/#preselection >>> >>> >>> Yet in the same page, at the top it says: >>> >>> Between 10 and 50 OSDs set pg_num to 4096 >>> >>> Our use is for shared hosting so there are lots of small writes and >>> reads. Which of these would be correct? >>> >>> Also is it a simple process to update PGs on a live system without >>> affecting service? >>> _______________________________________________ >>> 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 _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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