[openstack-dev] [openstack-operators][cinder] max_concurrent_builds in Cinder

Sean McGinnis sean.mcginnis at gmx.com
Tue May 24 01:51:20 UTC 2016

On Mon, May 23, 2016 at 05:32:45PM +0300, Ivan Kolodyazhny wrote:
> Hi developers and operators,
> I would like to get any feedback from you about my idea before I'll start
> work on spec.
> In Nova, we've got max_concurrent_builds option [1] to set 'Maximum number
> of instance builds to run concurrently' per each compute. There is no
> equivalent Cinder.

I do think it would be worth having some sort of operation throttling.

So are you thinking something more the "maximum number of volume builds
to run concurrently"? As you point out below, there are other operations
besides the creation that can cause problems when run in bulk.

I do like the idea!

> Why do we need it for Cinder? IMO, it could help us to address following
> issues:
>    - Creation of N volumes at the same time increases a lot of resource
>    usage by cinder-volume service. Image caching feature [2] could help us a
>    bit in case when we create volume form image. But we still have to upload N
>    images to the volumes backend at the same time.
>    - Deletion on N volumes at parallel. Usually, it's not very hard task
>    for Cinder, but if you have to delete 100+ volumes at once, you can fit
>    different issues with DB connections, CPU and memory usages. In case of
>    LVM, it also could use 'dd' command to cleanup volumes.
>    - It will be some kind of load balancing in HA mode: if cinder-volume
>    process is busy with current operations, it will not catch message from
>    RabbitMQ and other cinder-volume service will do it.
>    - From users perspective, it seems that better way is to create/delete N
>    volumes a bit slower than fail after X volumes were created/deleted.
> [1]
> https://github.com/openstack/nova/blob/283da2bbb74d0a131a66703516d16698a05817c7/nova/conf/compute.py#L161-L163
> [2]
> https://specs.openstack.org/openstack/cinder-specs/specs/liberty/image-volume-cache.html
> Regards,
> Ivan Kolodyazhny,
> http://blog.e0ne.info/

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