Disable multi-attach for RBD

[Eric Harney]

The multi-attach flag was set to True for the RBD driver in bug 1519227 with this commit:

https://review.openstack.org/#/c/249080/

But this did not consider the checks that need to be done related to RBD features to ensure that multi-attach can actually be safely used. Currently, RBD deployments using multi-attach are at risk due to this allowing invalid configurations.

The driver needs to disable RBD features that are not compatible with multi-attach. This may involve adding an option for deployers to choose whether or not they wish to support RBD multi-attach since there is a tradeoff between that functionality and other performance optimizations.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/283695

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/283695
Committed: https://git.openstack.org/cgit/openstack/cinder/commit/?id=59a22e3d3e002d29d9ed2dcd3c1c7578c4632c79
Submitter: Jenkins
Branch: master

commit 59a22e3d3e002d29d9ed2dcd3c1c7578c4632c79
Author: Eric Harney <email address hidden>
Date: Tue Feb 23 11:51:40 2016 -0500

    Disable multi-attach for RBD

    This is not really safe to turn on yet, as there
    are RBD features which are incompatible with
    multi-attach that must be managed from Cinder.

    Disable multi-attach for now until code to handle
    that is ready.

    Change-Id: I17da2f4e897178762d1c3d1302d2d79ae28e349c
    Related-Bug: #1519227
    Partial-Bug: #1535815

[Xuepeng Ji (ji-xuepeng)]

I want to know what kind of risk I will encounter if multi-attach flag is set in RBD driver, and which RBD feature is related with multi-attach?
In our production, VMs which run in HA mode may attach the same volume as data volume, but at same time only one VM can access to the volume. Can I enable multi-attach in RBD driver in this scenario.

[Eric Harney (eharney)]

I'm closing this bug as there isn't any high priority fix needed here for now -- the remaining work is to implement multi-attach as a feature for the RBD driver which can be tracked elsewhere.

[Eric Harney (eharney)]

This was actually fixed in Liberty, but I can't target it there now, so listing as o-1.

[yao ning (mslovy11022)]

Hi, eharney. Can you explicitly point out that which features in ceph will make this feature unsafe?

As a Contributor in ceph community, I may help to solve the dependency and make this feature available, thanks.

By the way, we enable this feature in our own branch and use this feature for several months. we do not find any problems when running Oracle OCFS2 based on mutiattach features. So can you kindly provide the BUG report when enabling this feature, or any links show enabling this feature will lead to unsafe?