Btw, the original discussion leading to the 4% recommendation is here: https://github.com/ceph/ceph/pull/23210 -- Paul Emmerich Looking for help with your Ceph cluster? Contact us at https://croit.io croit GmbH Freseniusstr. 31h 81247 München www.croit.io Tel: +49 89 1896585 90 On Thu, Aug 15, 2019 at 11:23 AM Виталий Филиппов <vitalif@xxxxxxxxxx> wrote: > > 30gb already includes WAL, see http://yourcmc.ru/wiki/Ceph_performance#About_block.db_sizing > > 15 августа 2019 г. 1:15:58 GMT+03:00, Anthony D'Atri <aad@xxxxxxxxxxxxxx> пишет: >> >> Good points in both posts, but I think there’s still some unclarity. >> >> Absolutely let’s talk about DB and WAL together. By “bluestore goes on flash” I assume you mean WAL+DB? >> >> “Simply allocate DB and WAL will appear there automatically” >> >> Forgive me please if this is obvious, but I’d like to see a holistic explanation of WAL and DB sizing *together*, which I think would help folks put these concepts together and plan deployments with some sense of confidence. >> >> We’ve seen good explanations on the list of why only specific DB sizes, say 30GB, are actually used _for the DB_. >> If the WAL goes along with the DB, shouldn’t we also explicitly determine an appropriate size N for the WAL, and make the partition (30+N) GB? >> If so, how do we derive N? Or is it a constant? >> >> Filestore was so much simpler, 10GB set+forget for the journal. Not that I miss XFS, mind you. >> >> >>>> Actually standalone WAL is required when you have either very small fast >>>> device (and don't want db to use it) or three devices (different in >>>> performance) behind OSD (e.g. hdd, ssd, nvme). So WAL is to be located >>>> at the fastest one. >>>> >>>> For the given use case you just have HDD and NVMe and DB and WAL can >>>> safely collocate. Which means you don't need to allocate specific volume >>>> for WAL. Hence no need to answer the question how many space is needed >>>> for WAL. Simply allocate DB and WAL will appear there automatically. >>>> >>>> >>> Yes, i'm surprised how often people talk about the DB and WAL separately >>> for no good reason. In common setups bluestore goes on flash and the >>> storage goes on the HDDs, simple. >>> >>> In the event flash is 100s of GB and would be wasted, is there anything >>> that needs to be done to set rocksdb to use the highest level? 600 I >>> believe >> >> ________________________________ >> ceph-users mailing list >> ceph-users@xxxxxxxxxxxxxx >> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > > > -- > With best regards, > Vitaliy Filippov > _______________________________________________ > 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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