On Thu, Jun 14, 2018 at 11:04 AM Lars Marowsky-Bree <lmb@xxxxxxxx> wrote:
Hi all,
so, I'm wondering right now (with some urgency, ahem) how to make RBD on
EC pools faster without resorting to cache tiering.
In a replicated pool, we had some success with RBD striping.
I wonder if it would be possible to align RBD stripe-unit with the EC
chunk size ...?
Is that worth pursuing at all? How would one best go about this?
Yes, you should do this. I think the RADOS code in a recent-ish release fixed things so that it doesn’t allow the EC stripes to be quite as misaligned as before, but it’s still not trying to target anything particularly efficient. I imagine you’d just set it up so that object size divided by k is an even power of two of reasonable size...?
(I also wonder if the
http://docs.ceph.com/docs/master/rados/operations/erasure-code-profile/
description of stripe_unit / stripe_width is wrong - shouldn't that be
the number of data+coding chunks, instead of just data chunks? They
need to go somewhere, right?)
Align k+m and RBD's object_size / (stripe-unit * stripe_count)?
Well, if you set an object to 4MB that will be the size of the raw data fed in, right? So if you have 4+2 coding there will be 6 chunks of 1MB each.
-Greg
Regards,
Lars
--
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
"Architects should open possibilities and not determine everything." (Ueli Zbinden)
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