Hello Kai,
Zitat von Kai Krakow <hurikhan77@xxxxxxxxx>:
Am Tue, 07 Feb 2017 13:35:58 +0100
schrieb "Jens-U. Mozdzen" <jmozdzen@xxxxxx>:
Hi *,
[...]
If it is about block sizes, questions pile up: Are the "dos" and
"don'ts" documented anywhere? It's a rather common situation for us
to run multiple backing devices on a single cache set, with both
complete HDDs and logical volumes as backing stores. So it's very
easy to come into a situation where we see either different block
sizes between backing store and caching device or even differing
block sizes between the various backing stores.
- using 512b for cache and 4k for backing device seems not to work,
unless above is purely a size limit problem
- 512b for cache and 512b for backing store seems to work
- 4k for cache and 4k for backing store will probably work as well
- will 4k for cache and 512b for backing store work (sounds likely,
as there will be no alignment problem in the backing store. OTOH,
will bcache try to write 4k data (cache block) into 512b blocks
(backing store) or will it write 8 blocks then, mapping the block
size differences?)
- if the latter works, will using both 4k and 512b backing stores in
parallel work if using a 4k cache?
Any insight and/or help tracking down the error are most welcome!
Hmm, I think for me it refused to attach backend and cache if block
sizes differ. So I think the bug is there...
Once I created backing store and cache store in two separate steps.
During attaching, it complained that block sizes don't match and the
cacheset cannot be attached.
hm, I believe to have created the backing store and cache set in a
common call to make-bcache for the mentioned server 2 and 3 - usually,
I only attach separately when creating additional backing stores for
an existing cache set. Currently I have no server to test, though.
Attaching differingly block-sized cache sets definitely works for me,
both kernel 4.1.36 and 4.9.8.
So you're saying that block sizes need to match? Then I'm in trouble,
as I have SAS SSDs with 512b and HDDs with 4k block size that build
the main storage for the environment in question.
Regards,
Jens
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