On Sat, Apr 4, 2020 at 4:13 PM <jesper@krogh.cc> wrote:
Offloading the block.db on NVMe / SSD: https://docs.ceph.com/docs/mimic/rados/configuration/bluestore-config-ref/
Pro: Easy to deal with - seem heavily supported. Con: As far as I can tell - this will only benefit the metadata of the osd- not actual data. Thus a data-commit to the osd til still be dominated by the writelatency of the underlying - very slow HDD.
small writes (<= 32kb, configurable) are written to db first and written back to the slow disk asynchronous to the original request.
Now, that sounds really interesting - I havent been able to find that in the documentation - can you provide a pointer? Whats the configuratoin parameter named? Meaning moving block.dk to a say 256GB NVMe will do "the right thing" for the system and deliver a fast write cache for smallish writes. Would setting the parameter til 1MB be "insane"? Jesper