[openstack-dev] [cinder] making volume available without stopping VM

Jay Bryant jsbryant at electronicjungle.net
Sat Jun 23 17:41:30 UTC 2018


On Sat, Jun 23, 2018, 9:39 AM Volodymyr Litovka <doka.ua at gmx.com> wrote:

> Dear friends,
>
> I did some tests with making volume available without stopping VM. I'm
> using CEPH and these steps produce the following results:
>
> 1) openstack volume set --state available [UUID]
> - nothing changed inside both VM (volume is still connected) and CEPH
> 2) openstack volume set --size [new size] --state in-use [UUID]
> - nothing changed inside VM (volume is still connected and has an old size)
> - size of CEPH volume changed to the new value
> 3) during these operations I was copying a lot of data from external
> source and all md5 sums are the same on both VM and source
> 4) changes on VM happens upon any kind of power-cycle (e.g. reboot
> (either soft or hard): openstack server reboot [--hard] [VM uuid] )
> - note: NOT after 'reboot' from inside VM
>
> It seems, that all these manipilations with cinder just update internal
> parameters of cinder/CEPH subsystems, without immediate effect for VMs.
> Is it safe to use this mechanism in this particular environent (e.g.
> CEPH as backend)?
>
>  From practical point of view, it's useful when somebody, for example,
> update project in batch mode, and will then manually reboot every VM,
> affected by the update, in appropriate time with minimized downtime
> (it's just reboot, not manual stop/update/start).
>
> Thank you.
>
> --
> Volodymyr Litovka
>    "Vision without Execution is Hallucination." -- Thomas Edison
>
>
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Volodymyr,

We have had similar issues with extending attached volumes that are iSCSI
based. In that case the VM has to be forced to rescan the scsi bus.

In this case I am not sure if there needs to be a change to Libvirt or to
rbd or something else.

I would recommend reaching out to John Bernard for help.

Jay

>
>
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