LVM on top of linux zfs to use Openstack with nova-volume

LVM on top of linux zfs to use Openstack with nova-volume

Did you ever wanted to know how to setup LVM on top of linux zfs to use Openstack with nova-volume? In this article i will describe this in a few easy steps based on my earlier mentioned how to about zfs on linux.

A common problem when using ZFS as storage for openstack is the lack of plugins that will cover as interface between nova-volume/cinder-volume and the block storage types. The volume service needs an LVM Volume group called nova-volumes as default.

In this how-to i will explain you step by step a workaround how to create an block storage device with zfs and get it into lvm.

Prerequisites:

• ZFS on Openstack
• LVM
• nova-volume or cinder-volume

Create a ZFS filesystem you will later use as LVM Group:

zfs create -V 500G storage/your_new_volume

The -V switch defines the size of the new created file-system. Change “storage” to you pool name.

Lets see how it looks like:

zfs list

Command Output:
NAME                            USED  AVAIL  REFER  MOUNTPOINT
storage/your_new_volume   516G  1.78T    76K  -

There you see your new created file-system without an mountpoint.

We now need to get its real device path:

file /dev/zvol/storage/your_new_volume

Command output: 
/dev/zvol/storage/your_new_volume: symbolic link to `../../zd0'

So our real device path is: /dev/zd0

Let’s do the magic part:

losetup /dev/loop2 /dev/zd0

And create a partition on that device:

fdisk /dev/loop2
(and hit: n p 1 ENTER ENTER t 8e w)

Finally we can create our LVM volume group:

pvcreate /dev/loop2
vgcreate nova-volumes /dev/loop2

We now need to make clear that the loop device gets mounted on the next boot:

Modify the file called /etc/rc.local in your preferred editor and enter following:

exec losetup /dev/loop2 /dev/zd0

And that’s it!