[large-scale][cinder] backend_native_threads_pool_size option with rbd backend

Rajat Dhasmana rdhasman at redhat.com
Tue Jul 5 16:06:14 UTC 2022

Hi Arnaud,

We discussed this in last week's cinder meeting and unfortunately we
haven't tested it thoroughly so we don't have any performance numbers to
What we can tell is the reason why RBD requires a higher number of native
threads. RBD calls C code which could potentially block green threads hence
blocking the main operation therefore all of the calls in RBD to execute
operations are wrapped to use native threads so depending on the operations
we want to
perform concurrently, we can set the value of
backend_native_threads_pool_size for RBD.

Thanks and regards
Rajat Dhasmana

On Mon, Jun 27, 2022 at 9:35 PM Arnaud Morin <arnaud.morin at gmail.com> wrote:

> Hey all,
> Is there any recommendation on the number of threads to use when using
> RBD backend (option backend_native_threads_pool_size)?
> The doc is saying that 20 is the default but it should be increased,
> specially for the RBD driver, but up to which value?
> Is there anyone tuning this parameter in their openstack deployments?
> If yes, maybe we can add some recommendations on openstack large-scale
> doc about it?
> Cheers,
> Arnaud.
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