On 8/14/19 1:06 PM, solarflow99 wrote:

    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
    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
    for WAL. Hence no need to answer the question how many space is
    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

When you first setup the OSD you could manually tweak the level sizes/multipliers so that one of the level boundaries + WAL falls somewhat under the total allocated size of the DB device.  Keep in mind that there can be temporary space usage increases due to compaction.  Ultimately though I think this is a bad approach. The better bet is the work that Igor and Adam are doing:




ceph-users mailing list

Reply via email to