I suggest having a look at this thread, which suggests that sizes 'in between' the requirements of different RocksDB levels have no net effect, and size accordingly. http://lists.ceph.com/pipermail/ceph-users-ceph.com/2018-October/030740.html My impression is that 28GB is good (L0+L1+L3), or 280 GB is good (+L4 too), or whatever size is required for +L5 is good, but anything in between will probably not get used. I've seen this somewhat borne out with our oldest storage nodes which have only enough NVMe space to provide 24GB per OSD. Though only ~3GiB of DB space are in use of the 24GiB available, 1GiB of 'slow db' is used: "db_total_bytes": 26671570944, "db_used_bytes": 2801795072, "slow_used_bytes": 1102053376 (Mimic 13.2.5) thanks, Ben On Tue, May 28, 2019 at 12:55 PM Igor Fedotov <ifedotov@xxxxxxx> wrote: > > Hi Jake, > > just my 2 cents - I'd suggest to use LVM for DB/WAL to be able > seamlessly extend their sizes if needed. > > Once you've configured this way and if you're able to add more NVMe > later you're almost free to select any size at the initial stage. > > > Thanks, > > Igor > > > On 5/28/2019 4:13 PM, Jake Grimmett wrote: > > Dear All, > > > > Quick question regarding SSD sizing for a DB/WAL... > > > > I understand 4% is generally recommended for a DB/WAL. > > > > Does this 4% continue for "large" 12TB drives, or can we economise and > > use a smaller DB/WAL? > > > > Ideally I'd fit a smaller drive providing a 266GB DB/WAL per 12TB OSD, > > rather than 480GB. i.e. 2.2% rather than 4%. > > > > Will "bad things" happen as the OSD fills with a smaller DB/WAL? > > > > By the way the cluster will mainly be providing CephFS, fairly large > > files, and will use erasure encoding. > > > > many thanks for any advice, > > > > Jake > > > > > > _______________________________________________ > > 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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