On 30-1-2017 10:17, Kostas Liakakis wrote: > On 2017-01-29 22:09, Willem Jan Withagen wrote: >> The disadvantage is that there will be a double write per original write: >> (ceph) first write is to the journal-file >> (zfs) write is stored in the write queue >> (zfs) write to ZIL(ssd) if write is synced write >> (zfs) async write to disk when write slot is available >> (ceph) read from zfs-store, >> (zfs) delivers data either arc(ram) or l2arc(ssd) or HD >> (ceph) writes data to filestore. >> (zfs) write is stored in the write queue >> (zfs) write to ZIL(ssd) if write is synced write >> (zfs) async write to disk when write slot is available >> >> And I hoped to forgo the Ceph journal write/read cycle. > You've got a slight misconception there, not that it matters much to > your problem. > > A Ceph OSD will never read its journal under normal operation. OSD will > only commit data to the journal before it commits them to its filestore. > The journal is only replayed after an OSD crash or otherwise abnormal > termination. Ah, Oke .. Thanx for the clarification. This is also how ZFS does it. The ZIL is only read in case a node crashes and transactions need to be replayed. > The way Ceph OSDs w/ filestore has been put in place I don't think there > is a way to fully utilize zfs features. I'm running some benchmarks with a simple config just to see what is going on. And your explanation is in accordance with what I was seeing. Although I do see some reads from the journal, but not at the same rate things are written. Guess I'm going to be toying a bit more.... --WjW -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
