Hi all, let me join in on the question, even though the aspect I am looking for may be slightly different (I also asked earlier on the list without response). My question relates to the storage of metadata by CephFS MDS servers. They appear to use almost exclusively RocksDB, so my question is how much of this "RocksDB-I/O" would go to a WAL, and how much I/O would go to an SSD - i.e. would it be preferrable to separate out the WAL and buy a faster device for it? Also, is there a tuning parameter such as bluestore_prefer_deferred_size for this? Cheers, Oliver Am 09.03.2018 um 16:02 schrieb Budai Laszlo: > Hello Rich, > > I've seen your question on the ML, but I was hoping that after two more months, maybe we can get some feedback on this topic. > Regarding the WAL size, is there a way to specify the WAL and db partition size at the time of OSD preparation? > > Kind regards, > Laszlo > > > On 09.03.2018 14:47, Richard Hesketh wrote: >> I am also curious about this, in light of the reported performance regression switching from Filestore to Bluestore (when using SSDs for journalling/metadata db). I didn't get any responses when I asked, though. The major consideration that seems obvious is that this potentially hugely increases the required size for the WAL, but I'm not sure if that has any implications beyond simply needing a larger WAL/DB device or if there's other config changes that you'd need to do. >> >> Rich >> >> On 09/03/18 09:35, Budai Laszlo wrote: >>> Dear all, >>> >>> I am wondering whether it helps to increase the bluestore_prefer_deferred_size to 4MB so the RBD chunks are first written to the WAL, and only later to the spinning disks. >>> Any opinions/experiences about this? >>> >>> Kind regards, >>> Laszlo >>> >>> On 08.03.2018 18:15, Budai Laszlo wrote: >>>> Dear all, >>>> >>>> I'm reading about the bluestore_prefer_deferred_size parameter for Bluestore. Are there any hints about its size when using a dedicated SSD for bock.wal and block.db ? >>>> >>>> Thank you in advance! >>>> >>>> Laszlo >> >> >> >> _______________________________________________ >> 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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