Creating multiple servers with a shared volume

open infra openinfradn at gmail.com
Tue Sep 28 12:47:14 UTC 2021


On Mon, Sep 27, 2021 at 2:15 PM Lee Yarwood <lyarwood at redhat.com> wrote:

> On 25-09-21 13:11:19, open infra wrote:
> > On Sat, Sep 25, 2021 at 7:37 AM Laurent Dumont <laurentfdumont at gmail.com
> >
> > wrote:
> >
> > > Just to be sure, the flow is.
> > >
> > >    - Create VM with root disk on a volume/image.
> > >    - Create another 1TB volume.
> > >    - Attach the volume to the VM as a second drive using a multi attach
> > >    approach (
> > >
> https://docs.openstack.org/cinder/latest/admin/blockstorage-volume-multiattach.html
> > >    )?
> > >    - Create snapshot of the original VM (with it's root drive + 1 TB
> > >    volume)?
> > >    - Create new VM from snapshot.
> > >    - Instead of a new VM + 1 new root volume + the same 1TB multiattach
> > >    volume attached, you get a new multiattach volume (new volume ID and
> > >    everything)?
>
> Because you're attaching a snapshot and not the original volume? See
> below for more.
>
> > Yes, here is the block device mapping of the snapshot (from a VM with
> 100GB
> > of root disk and 1TB of multiattach volume)
> >
> > block_device_mapping[{"image_id": null, "delete_on_termination": true,
> > "device_name": "/dev/vda", "disk_bus": "virtio", "volume_id": null,
> > "volume_type": null, "destination_type": "volume", "source_type":
> > "snapshot", "guest_format": null, "volume_size": 100, "device_type":
> > "disk", "snapshot_id": "7b2c7f3a-8420-4a33-820e-2d2231d930c7",
> > "boot_index": 0, "no_device": null, "tag": null}, {"image_id": null,
> > "delete_on_termination": false, "device_name": "/dev/vdb", "disk_bus":
> > null, "volume_id": null, "volume_type": null, "destination_type":
> "volume",
> > "source_type": "snapshot", "guest_format": null, "volume_size": 1000,
> > "device_type": null, "snapshot_id":
> "c2a0695f-8c9e-46f9-80a8-560c47521eeb",
> > "boot_index": null, "no_device": null, "tag": null}]
>
> As you can see above you're using source_type = "snapshot" and
> destination_type of "volume". As set out in the following docs this
> creates a new volume from a given snapshot and attaches that to the
> instance:
>
>
> https://docs.openstack.org/nova/latest/user/block-device-mapping.html#valid-source-destination-combinations
>
> snapshot -> volume - this works exactly as passing type=snap does. It
> would create a volume from a Cinder volume snapshot and attach that
> volume to the instance. Can be marked bootable.
>
>
> https://docs.openstack.org/api-ref/compute/?expanded=create-server-detail#create-server
>
> block_device_mapping_v2.source_type (Optional)
>
> The source type of the block device. Valid values are:
> [..]
> snapshot: This is only valid with destination_type=volume; creates a
> volume backed by the given volume snapshot referenced via the
> block_device_mapping_v2.uuid parameter and attaches it to the server
>
> When attaching multiattach enabled volumes to multiple instances you
> need to use source_type = 'volume' *and* destination_type = 'volume'.
>
> Hope this helps,
>


It very clears what went wrong.
The above block device mapping was found when I try to figure out what went
wrong.
But I am not sure where exactly I should define block device mapping when I
use CLI.
Appreciate if you can give an example.

Thanks a lot Lee Yarwood!


>
> --
> Lee Yarwood                 A5D1 9385 88CB 7E5F BE64  6618 BCA6 6E33 F672
> 2D76
>
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