Refreshing a VM configuration from a vVol Snapshot

A lot of the time when we talk about vVols and snapshots we talk about restoring the virtual disks (the data vVols). This of course is a huge benefit of vVols–the virtual disks are 1:1 to a volume on the array so the snapshots (and other array features) can be used at a level of virtual disk. Need to restore a database on virtual disk B (the E:\ drive or whatever), just use the snapshot restore to instantly refresh the entire disk. No need to mount a copied datastore, resignature, remove the old disk etc. etc. Just copy from the snapshot to the vVol volume and re-mount the file system in the guest. Fast and easy.

VMware snapshots exist with vVols too–they create array-based copies. But when you restore from them, you restore the whole VM. And the existence of them complicate the VM configuration–extra pointers and files etc. So a common vVol option is to just temporarily use VMware snapshots for backup procedures or for one off protection of VMs while I run an upgrade etc and then delete it when it works.

What if I want to refresh the VM configuration from a snapshot? Keep the data on the disk as is, but refresh the VM config files (VMX mainly) from a snapshot?

This is possible from a VMFS but quite complex. For a vVol VM this is really simple. Process?

  1. Shutdown VM.
  2. Copy from snapshot to config volume.
  3. Reload VMX
  4. Power-on VM.

So for some background, in a vVol world the VM directory (which houses the VMX file, some logs, virtual disk pointers, and some other frivolities) looks like a folder. But in reality it is a logical pointer to a volume on the array. This volume is called a config vVol and each “directory” in the vVol datastore maps to one. This config vVol is actually a mini VMFS. See more details here

Since this is a volume, you can of course take snapshots of it. There are a few ways to do this, either create one off snapshots of it or through protection policies.

Continue reading “Refreshing a VM configuration from a vVol Snapshot”

Affecting Persistent Volumes in VMware Tanzu

Note: This is another guest blog by Kyle Grossmiller. Kyle is a Sr. Solutions Architect at Pure and works with Cody on all things VMware.

VMware Tanzu is a game-changing piece of technology for numerous reasons, but probably the most transformational piece of it is also the most apparent – it provides the capability for the vCenter admin to give resources for both consumers of traditional virtual machines as well as Kubernetes/DevOps users from the same set of compute hosts and storage. This consolidation means that the vCenter admin can more easily see what is being allocated where, as well as gaining insight into what application(s) might be candidates to make the move into a container-based environment from a virtual machine.

A Tanzu deployment is comprised of quite a few moving pieces and a central piece of this is durable storage made possible by persistent volumes. While container nodes and pods are ephemeral by nature (which is one of their major advantages), the data that they consume, produce and manipulate must be performant, portable and often, saved. So, there is obviously a different set of things we care about for persistent data vs the Kubernetes nodes that Tanzu runs in unison with here. For the remainder of this post we will show a couple of quick and easy ways you can change your persistent volumes to suit your application needs. There’s a bit of work and some choices to be made around getting a Tanzu environment up and running in vSphere, and I’d encourage you to check out the VMware Tanzu User Guide on our Pure Storage support site or Cody’s blog series to get some additional information.

With that being said, when a persistent volume is created via either dynamic or static provisioning, one of the first things the application developer needs to decide is what will happen to that volume and data when the application that uses it itself is no longer needed. The default behavior for an SPBM policy/storageclass assigned to a vSphere Namespace is to delete it, but through a simple kubectl patch command line, the persistent volume can be saved for future usage.

To make this change, first get the persistent volume name that you want to Retain/save:

 
$ kubectl get pv
 NAME           CAPACITY    RECLAIM POLICY   STATUS 
 pvc-f37c39fd   5Gi         Delete           Bound 

Next, apply this kubectl command line to it to switch the reclaim policy from Delete to Retain:

‚Äč$ kubectl patch pv (PV_Name) -p '{"spec":{"persistentVolumeReclaimPolicy":"Retain"}}'

So for our PV example:

$ kubectl patch pv pvc-f37c39fd -p '{"spec":{"persistentVolumeReclaimPolicy":"Retain"}}'

When we run the kubectl get pv command again, we can see it is set to Retain, so we are all set:

$ kubectl get pv
NAME           CAPACITY    RECLAIM POLICY   STATUS  
pvc-f37c39fd   5Gi         Retain           Bound          

If there is anything close to a certainty in the storage world – it is that the longer a volume exists, the more full of data it will become. This becomes even more of a certainty if a persistent volume is retained and reused across multiple application instances for increasing amounts of time. In the vSphere and Supervisor cluster 7.0U2 release VMware has introduced the capability for Online Volume Expansion. What this means is that while in previous versions users had to unbind their persistent volume claim from a pod or node prior to resizing it (otherwise known as offline volume expansion) – now they are able to accomplish that same operation without that step . This is a huge advantage as the offline expansion required that the volume be effectively be taken out of service when additional space was added to it, which could lead to application downtime. With the online volume expansion enhancement that annoyance goes away completely.

Online volume expansion operation is really simple to do. This time we find the persistent volume claim (which is basically the glue between the persistent volume and the application) that we need to expand:

$ kubectl get pvc
NAME             STATUS  VOLUME        CAPACITY
pvc-vvols-mysql  Bound   pvc-f37c39fd  5Gi      

Now we run the following patch command against the PVC name we found above so that it knows to request additional storage for the persistent volume that it is bound to. In this case, we will ask to expand from 5Gi to 6Gi:

$ kubectl patch pvc pvc-vvols-mysql -p '{"spec": {"resources": {"requests":{"storage": "6Gi"}}}}'

After waiting for a few moments for the expansion to complete, we look at the pvc in order to confirm we have the additional space that we asked for and we can see it has been added:

$ kubectl get pvc
NAME              STATUS   VOLUME         CAPACITY
pvc-vvols-mysql   Bound    pvc-f37c39fd   6Gi     

Taking a closer look at the PVC via the describe command shows that it indeed increased the PV size while it remained mounted to the mysql-deployment node under the events section:

$ kubectl describe pvc
Name:          pvc-vvols-mysql
Namespace:     default
StorageClass:  cns-vvols
Status:        Bound
Volume:        pvc-f37c39fd-dbe9-4f27-abe8-bca85bf9e87c
Labels:        <none>
Annotations:   pv.kubernetes.io/bind-completed: yes
               pv.kubernetes.io/bound-by-controller: yes
               volume.beta.kubernetes.io/storage-provisioner: csi.vsphere.vmware.com
               volumehealth.storage.kubernetes.io/health: accessible
Finalizers:    [kubernetes.io/pvc-protection]
Capacity:      6Gi
Access Modes:  RWO
VolumeMode:    Filesystem
Mounted By:    mysql-deployment-5d8574cb78-xhhq5
Events:
  Type     Reason                      Age   From                                             Message
  ----     ------                      ----  ----                                             -------
  Warning  ExternalExpanding           52s   volume_expand                                    Ignoring the PVC: didn't find a plugin capable of expanding the volume; waiting for an external controller to process this PVC.
  Normal   Resizing                    52s   external-resizer csi.vsphere.vmware.com          External resizer is resizing volume pvc-f37c39fd-dbe9-4f27-abe8-bca85bf9e87c
  Normal   FileSystemResizeRequired    51s   external-resizer csi.vsphere.vmware.com          Require file system resize of volume on node
  Normal   FileSystemResizeSuccessful  40s   kubelet, tkc-120-workers-mbws2-68d7869b97-sdkgh  MountVolume.NodeExpandVolume succeeded for volume "pvc-f37c39fd-dbe9-4f27-abe8-bca85bf9e87c"

Those are just a couple of the ways we can update our persistent volumes to do what we need them to do within a Tanzu deployment, and we have really just scratched the surface with these few examples. To see how to do more advanced operations like migrating a persistent volume to a different Tanzu Kubernetes Cluster, please head over to our new Tanzu User Guide. Of course, it also is very important to mention that Portworx combined with Tanzu gives us even more features and functionalities like RBAC, automated backup and recovery and a whole lot more. Getting deeper into how Portworx interoperates with Tanzu is what I’m working on next so please stay tuned for some more cool stuff.