30gb already includes WAL, see
http://yourcmc.ru/wiki/Ceph_performance#About_block.db_sizing
15 августа 2019 г. 1:15:58 GMT+03:00, Anthony D'Atri <a...@dreamsnake.net>
пишет:
>Good points in both posts, but I think there’s still some unclarity.
>
>Absolutely let’s talk about DB and WAL together. By “bluestore goes on
>flash” I assume you mean WAL+DB?
>
>“Simply allocate DB and WAL will appear there automatically”
>
>Forgive me please if this is obvious, but I’d like to see a holistic
>explanation of WAL and DB sizing *together*, which I think would help
>folks put these concepts together and plan deployments with some sense
>of confidence.
>
>We’ve seen good explanations on the list of why only specific DB sizes,
>say 30GB, are actually used _for the DB_.
>If the WAL goes along with the DB, shouldn’t we also explicitly
>determine an appropriate size N for the WAL, and make the partition
>(30+N) GB?
>If so, how do we derive N? Or is it a constant?
>
>Filestore was so much simpler, 10GB set+forget for the journal. Not
>that I miss XFS, mind you.
>
>
>>> 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
>
>
>
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--
With best regards,
Vitaliy Filippov
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