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
located
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
volume
for WAL. Hence no need to answer the question how many space is
needed
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:
https://github.com/ceph/ceph/pull/28960
https://github.com/ceph/ceph/pull/29047
Mark
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