On Fri, Mar 29, 2019 at 1:48 AM Christian Balzer <chibi@xxxxxxx> wrote: > > On Fri, 29 Mar 2019 01:22:06 -0400 Erik McCormick wrote: > > > Hello all, > > > > Having dug through the documentation and reading mailing list threads > > until my eyes rolled back in my head, I am left with a conundrum > > still. Do I separate the DB / WAL or not. > > > You clearly didn't find this thread, most significant post here but read > it all: > http://lists.ceph.com/pipermail/ceph-users-ceph.com/2019-March/033799.html > > In short, a 30GB DB(and thus WAL) partition should do the trick for many > use cases and will still be better than nothing. > Thanks for the link. I actually had seen it, but since it contained the mention of the 4%, and my OSDs are larger than those of the original poster there, I was still concerned that antying I could throw at it would be insufficient. I have a few OSDs that I've created with DB on the device, and this is what it ended up with after backfilling: Smallest: "db_total_bytes": 320063143936, "db_used_bytes": 1783627776, Biggest: "db_total_bytes": 320063143936, "db_used_bytes": 167883309056, So given that The biggest is ~160GB in size already, I wasn't certain if it would be better to have some with only ~20% of it split off onto an SSD, or leave it all together on the slower disk. I have a new cluster I"m building out with the same hardware, so I guess I'll see how it goes with a small DB unless anyone comes back and says it's a terrible idea ;). -Erik > Christian > > > I had a bunch of nodes running filestore with 8 x 8TB spinning OSDs > > and 2 x 240 GB SSDs. I had put the OS on the first SSD, and then split > > the journals on the remaining SSD space. > > > > My initial minimal understanding of Bluestore was that one should > > stick the DB and WAL on an SSD, and if it filled up it would just > > spill back onto the OSD itself where it otherwise would have been > > anyway. > > > > So now I start digging and see that the minimum recommended size is 4% > > of OSD size. For me that's ~2.6 TB of SSD. Clearly I do not have that > > available to me. > > > > I've also read that it's not so much the data size that matters but > > the number of objects and their size. Just looking at my current usage > > and extrapolating that to my maximum capacity, I get to ~1.44 million > > objects / OSD. > > > > So the question is, do I: > > > > 1) Put everything on the OSD and forget the SSDs exist. > > > > 2) Put just the WAL on the SSDs > > > > 3) Put the DB (and therefore the WAL) on SSD, ignore the size > > recommendations, and just give each as much space as I can. Maybe 48GB > > / OSD. > > > > 4) Some scenario I haven't considered. > > > > Is the penalty for a too small DB on an SSD partition so severe that > > it's not worth doing? > > > > Thanks, > > Erik > > _______________________________________________ > > ceph-users mailing list > > ceph-users@xxxxxxxxxxxxxx > > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > > > > > -- > Christian Balzer Network/Systems Engineer > chibi@xxxxxxx Rakuten Communications _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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