Hi Mark, thanks for your reply! I'm a big fan of keeping things simple - this means that there has to be a very good reason to put the WAL and DB on a separate device otherwise I'll keep it collocated (and simpler).
as far as I understood - putting the WAL,DB on a faster (than hdd) device makes more sense in cephfs and rgw environments (more metadata) - and less sense in rbd environments - correct? br wolfgang On 11/08/2017 02:21 PM, Mark Nelson wrote: > Hi Wolfgang, > > In bluestore the WAL serves sort of a similar purpose to filestore's > journal, but bluestore isn't dependent on it for guaranteeing > durability of large writes. With bluestore you can often get higher > large-write throughput than with filestore when using HDD-only or > flash-only OSDs. > > Bluestore also stores allocation, object, and cluster metadata in the > DB. That, in combination with the way bluestore stores objects, > dramatically improves behavior during certain workloads. A big one is > creating millions of small objects as quickly as possible. In > filestore, PG splitting has a huge impact on performance and tail > latency. Bluestore is much better just on HDD, and putting the DB and > WAL on flash makes it better still since metadata no longer is a > bottleneck. > > Bluestore does have a couple of shortcomings vs filestore currently. > The allocator is not as good as XFS's and can fragment more over time. > There is no server-side readahead so small sequential read performance > is very dependent on client-side readahead. There's still a number of > optimizations to various things ranging from threading and locking in > the shardedopwq to pglog and dup_ops that potentially could improve > performance. > > I have a blog post that we've been working on that explores some of > these things but I'm still waiting on review before I publish it. > > Mark > > On 11/08/2017 05:53 AM, Wolfgang Lendl wrote: >> Hello, >> >> it's clear to me getting a performance gain from putting the journal on >> a fast device (ssd,nvme) when using filestore backend. >> it's not when it comes to bluestore - are there any resources, >> performance test, etc. out there how a fast wal,db device impacts >> performance? >> >> >> br >> wolfgang >> > _______________________________________________ > ceph-users mailing list > ceph-users@lists.ceph.com > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com _______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
