> -----Original Message----- > From: ceph-devel-owner@xxxxxxxxxxxxxxx [mailto:ceph-devel- > owner@xxxxxxxxxxxxxxx] On Behalf Of Nathan Cutler > Sent: Thursday, September 22, 2016 10:03 PM > To: ceph-devel@xxxxxxxxxxxxxxx > Subject: OSD journal sizing > > I've been researching OSD journals lately, and just realized something that's > not particularly nice. > > SSDs are getting bigger and bigger. It's typical for customers to use e.g. a > 500GB SSD for their journals. If the OSDs themselves are on spinners, there is > no use in having journals bigger than 10GB because the 7200 RPMs impose a > hard ceiling on throughput that spinners can achieve. > > Now, SSDs need wear-leveling to avoid premature failure. If only a small > region of the SSD is partitioned/used, users may fear (regardless of the > reality, whatever it may be) that this small region will be "pummeled to > death" by Ceph and cause the expensive SSD to fail prematurely. Generally SSDs do their own internal wear-leveling so this fear is pretty much unfounded. > > I *thought* this could be addressed by creating the journal partitions large > enough to fill the entire disk and using the "osd journal size" > parameter to limit how much disk capacity is actually used for journaling, but > now I just noticed that the "osd journal size" parameter "is ignored if the > journal is a block device, and the entire block device is used." > > And while working on http://tracker.ceph.com/issues/16878 it occurred to > me that large journals are not getting tested much. Is that a valid > assumption? > > Next week I plan to attempt to make a reproducer for the bug, and then try > to come up with a patch to fix it. Any ideas/pointers, either here or in the > tracker, would be appreciated. > > -- > Nathan Cutler > Software Engineer Distributed Storage > SUSE LINUX, s.r.o. > Tel.: +420 284 084 037 > -- > 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 ��.n��������+%������w��{.n����z��u���ܨ}���Ơz�j:+v�����w����ޙ��&�)ߡ�a����z�ޗ���ݢj��w�f
