All SSD storage and journals

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Hello,

as others have reported in the past and now having tested things here
myself, there really is no point in having journals for SSD backed OSDs on
other SSDs.

It is a zero sum game, because:
a) using that journal SSD as another OSD with integrated journal will
yield the same overall result performance wise, if all SSDs are the same.
And In addition its capacity will be made available for actual storage.
b) if the journal SSD is faster than the OSD SSDs it tends to be priced
accordingly. For example the DC P3700 400GB is about twice as fast (write)
and expensive as the DC S3700 400GB.

Things _may_ be different if one doesn't look at bandwidth but IOPS (though
certainly not in the near future in regard to Ceph actually getting SSDs
busy), but even there the difference is negligible when for example
comparing the Intel S and P models in write performance.
Reads are another thing, but nobody cares about those in journals. ^o^

Obvious things that come to mind in this context would be the ability to
disable journals (difficult, I know, not touching BTRFS, thank you) and
probably K/V store in the future.

Regards,

Christian
-- 
Christian Balzer        Network/Systems Engineer                
chibi@xxxxxxx   	Global OnLine Japan/Fusion Communications
http://www.gol.com/
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