[openstack-dev] [Cinder] Do you think we should introduce the online-extend feature to cinder ?

Zhangleiqiang zhangleiqiang at huawei.com
Tue Mar 4 02:50:23 UTC 2014

@john.griffith. Thanks for your information.

I have read the BP you mentioned ([1]) and have some rough thoughts about it.

As far as I know, the corresponding online-extend command for libvirt is "blockresize", and for Qemu, the implement differs among disk formats.

For the regular qcow2/raw disk file, qemu will take charge of the drain_all_io and truncate_disk actions, but for raw block device, qemu will only check if the *Actual* size of the device is larger than current size.

I think the former need more consideration, because the extend work is done by libvirt, Nova may need to do this first and then notify Cinder. But if we take allocation limit of different cinder backend drivers (such as quota, nfs_used_ratio, nfs_oversub_ratio, etc) into account, the workflow will be more complicated.

This scenario is not included by the Item 3 of BP ([1]), as it cannot be simply "just work" or notified by the compute node/libvirt after the volume is extended.

This regular qcow2/raw disk files are normally stored in file system based storage, maybe the Manila project is more appropriate for this scenario?


[1]: https://blueprints.launchpad.net/cinder/+spec/inuse-extend-volume-extension


Best Regards

From: John Griffith [mailto:john.griffith at solidfire.com]
Sent: Tuesday, March 04, 2014 1:05 AM
To: OpenStack Development Mailing List (not for usage questions)
Cc: Luohao (brian)
Subject: Re: [openstack-dev] [Cinder] Do you think we should introduce the online-extend feature to cinder ?

On Mon, Mar 3, 2014 at 2:01 AM, Zhangleiqiang <zhangleiqiang at huawei.com<mailto:zhangleiqiang at huawei.com>> wrote:
Hi, stackers:

        Libvirt/qemu have supported online-extend for multiple disk formats, including qcow2, sparse, etc. But Cinder only support offline-extend volumes currently.

    Offline-extend volume will force the instance to be shutoff or the volume to be detached. I think it will be useful if we introduce the online-extend feature to cinder, especially for the file system based driver, e.g. nfs, glusterfs, etc.

    Is there any other suggestions?



Best Regards

OpenStack-dev mailing list
OpenStack-dev at lists.openstack.org<mailto:OpenStack-dev at lists.openstack.org>

Hi Zhangleiqiang,

So yes, there's a rough BP for this here: [1], and some of the folks from the Trove team (pdmars on IRC) have actually started to dive into this.  Last I checked with him there were some sticking points on the Nova side but we should synch up with Paul, it's been a couple weeks since I've last caught up with him.

[1]: https://blueprints.launchpad.net/cinder/+spec/inuse-extend-volume-extension

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