[libvirt] [PATCH 2/2] rbd: optionally disable actual disk-usage during pool/volume refresh

[Daniel P. Berrangé]

On Mon, Mar 11, 2019 at 11:39:55AM -0400, jdillama at redhat.com wrote:
> From: Jason Dillaman <dillaman at redhat.com>
> 
> For pools with numerous volumes or very large volumes, the disk-usage
> calculation can take a non-trivial amount of time even with the
> fast-diff feature enabled (especially since the the usage is calculated
> serially for each image in the pool).
> 
> The "rbd:config_opts" node now supports a new libvirt-internal
> "libvirt_calculate_disk_usage" option which can be set to false to
> disable this calculation as needed.

The RBD namespace is not something we want to encourage applications
to use. It is supposed to be for hacks that are only used in testing
or QA, never in production. Essentially any usage is considered
unsupported for production.

This scalability problem sounds like something most likely to hit in
production envs, and as such we need a fully supportable solution.
This probably suggests making it a core part of the storage pool
schema, and extending its impl to other drivers too.

Regards,
Daniel
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