OpenStack Cinder Support in Platform9 for VMware

The next release of Platform9’s VMware integration brings OpenStack Cinder support in Platform9 for VMware vSphere environments using VMDK drivers. This exposes the existing datastore as a block storage backend. This article answers some of the questions related to cinder integration.

1. Which Datastore Will Be Used for Volume Creation?

Currently cinder block storage service will use all available datastore for creation of volumes. The ability to specify certain datastore for volume creation using SPBM (Storage Policy Based Management) is coming soon.

2. How are the Volumes created?

• Blank volume creation: When a blank volume is created, cinder service will only create a placeholder for the volume. The volume is actually created when it is attached to a VM. This allows cinder service to determine the best datastore to use for volume creation.

• Creating volume from another volume or snapshot: When creating a volume from another volume or snapshot of a volume it is immediately created and it is usually placed on the same datastore as the source volume.

• Creating volume from an image: For creating volumes from images only those images that have been uploaded using ‘glance image-create’ can be used. Currently vSphere templates cannot be used for creating volumes. The volume is immediately created on any datastore available. The volume is marked bootable and instances can be created from this volume.

3. How are the Volumes Attached to VMs?

Volumes are attached to instances as SCSI disks using LSI logic as adapter type. Using this adapter allows hot add and remove of disks from instances in VMware environment. Some of the guest OS may not be able to recognize that a new disk has been attached and may require a reboot. Users can configure their guest OS to detect changes in SCSI hosts.

For example:
Executing following commands on CentOS 6.x will allow detection of changes in SCSI devices without reboot –
List all SCSI hosts on instance using following command:

ls /sys/class/scsi_host

Sample output:

host0 host1

For all the host listed by above command run the following command:

echo "- - -" > /sys/class/scsi_host/<host listed above>/scan

After that all SCSI disks should have been detected and should be visible with following command:

fdisk -l

4. How Do Volume Snapshots Work?

Snapshotting a volume creates a vCenter snapshot. This snapshot cannot be used directly and user needs to create a volume from that snapshot.

5. Where Can I See the Volumes?

VMware vCenter 5.1 and 5.5 do not allow creation of disks without a VM. Hence all the volumes created through Platform9 create a VM which can then be used for creating volumes. This VM must always remain powered off and must not be deleted from vCenter directly. All the VMs that are being used as backing of volumes will be placed under the “pf9_cinder_volumes” folder on the vCenter. Also operations performed directly on vCenter such as detach the cinder volume disk and attaching it to a different VM can cause issues with cinder service.