Taking Managed Snapshots of vVol-based VMs

While the FlashArray GUI, REST, and CLI interfaces can be used for both per-VM and per-virtual disk vVol operations, a major advantage of vVols is management of vVols from within vCenter. VMware administrators can use the Web Client or any other VMware management tool to create array-based snapshots of vVol-based VMs.

New-Snapshot -Name NewSnapshot -Quiesce:$false -VM vVolVM -Memory:$false 

1. vSphere issues a Prepare to Snapshot Virtual Volume request to the VASA Provider
2. The VASA Provider ensures that the virtual volume is ready to have a managed snapshot taken
   1. On the FlashArray this is the step that the volumes are created with the data-vvol name with a -snap suffix
   2. If the VM has a policy and replication group associated with it, the data-snap volumes are placed in the protection group associated with that policy and replication group
3. The VASA Provider responds back to vSphere that the prepare operation has completed and provides a uuid for the snapshot
4. vSphere pauses the VM to ensure that no outstanding activity happens (Usually referred to as VM Stun time)
5. vSphere issues a Snapshot Virtual Volume request to the VASA Provider for each Data vVol that the VM has
6. The VASA provider copies out the data vVols to the managed snapshot
   1. On the FlashArray a purevol copy is issued where the data-vvol is copied out and overwrites the data-vvol-snap that was created during the prepare phase
   2. In vSphere 7.0 U3 and higher the Snapshot Virtual Volume request passes multiple vVol uuids as part of the request, which helps improve batching and performance at scale
7. The VASA provider responds back to vSphere that Snapshot Virtual Volume is complete
8. vSphere unpauses the VM (the VM is unstunned) and the managed snapshot operation is complete

   While this seems like a lot of steps and process at first, they typically will complete under a ms. The biggest goal that both VMware and Everpure has is to decrease the amount of calls and time it takes between when the VM is stunned, snapshot virtual volume is issued and then completed.

   Here is a view from the Snapshot Management for a normal snapshot that had completed.

   vSphere Client View - Snapshot Management View - Normal Snapshot

   Here is a view from the FlashArray that shows the new volume objects created for a managed snapshot.

   FlashArray GUI View - Managed Snapshot for vVols based VM

   Note:

   FlashArray volume names are auto-generated, but VMware tools list the snapshot name supplied by the VMware administrator.

   Creating a Managed Snapshot with Saved Memory

   If the VMware administrator selects Store the Virtual Machine’s Memory State, the underlying snapshot process is more complex.

   Memory snapshots generally take somewhat longer than non-memory ones because the ESXi host directs the array to create a memory vVol to which it writes the VM’s entire memory image. Creation time is proportional to the VM’s memory size.

   vSphere Client View - Managed Snapshot Wizard

   Normal Snapshots, Memory Snapshots and File Quiesced Snapshots will all cause a VM to pause briefly. A normal snapshot causing the smallest amount of "VM Stun" during the snapshot process. File Quiesced and Memory based snapshots can have a VM "Stun Time" that varies depending on how busy the VM is, how large the VM is sized (Memory or Storage) and the version of vSphere. Typically the stun time for a VM snapshot will be seconds, but a memory snapshot could vastly increase the amount of stun time if the VM is sized large and is very busy.

   The memory vVol in a VM’s volume group created as a consequence of a memory snapshot stores the VM’s active state (memory image). ArrayView 25 shows the volume group of a VM with a memory snapshot (vvol-test-a-VM-light-0011-92ecaac2-vg/Memory-f60d917b). The size of the memory vVol is the memory size of the VM’s memory image.

   FlashArray GUI View - Memory Managed Snapshot Object

   VMware flags a memory snapshot with a green play icon to indicate that it includes the VM’s memory state.

   vSphere Client View - Snapshot Management View - Memory Managed Snapshot

   Reverting a VM to a Managed Snapshot

   VMware management tools can revert VMs to snapshots taken by VMware. As with snapshot creation, reverting is identical for conventional and vVol-based VM snapshots.

   To restore a VM from a snapshot, from the Web Client Hosts & Clusters or VMs and Templates view, select the VM to be restored and click the Snapshots tab in the adjacent pane to display a list of the VM’s snapshots.

   Select the snapshot from which to revert, click the All Actions button, and select Revert to from the dropdown menu.

   vSphere Client View - Reverting a VM to a Managed Snapshot

   Subsequent steps differ slightly for non-memory and memory snapshots.

   Reverting a VM from a Non-memory Managed Snapshot

   The Revert to command displays a confirmation dialog. Click Yes to revert the VM to the selected snapshot.

   The array overwrites the VM’s data vVols from their snapshots. Any data vVols added to the VM after the snapshot was taken are unchanged.

   Before reverting a VM from a non-memory snapshot, VMware shuts the VM down. Thus, reverted VMs are initially powered off.

   Reverting a VM from Memory Managed Snapshot

   To revert a VM to a memory snapshot, the ESXi host first directs the array to restore the VM’s data vVols from their snapshots, and then binds the VM’s memory vVol and reloads its memory. Reverting a VM to a memory snapshot takes slightly longer and results in a burst of read activity on the array.

   A VM reverted to a memory snapshot can be reverted either suspended or to a running state. Check the Suspend this virtual machine when reverting to selected snapshot box in the Confirm Revert to Snapshot wizard to force the reverted VM to be powered off initially. If the box is not checked, the VM is reverted into its state at the time of the snapshot.

   FlashArray GUI View - Memory Snapshot Read IO

   Deleting a Managed Snapshot

   Snapshots created with VMware management tools can be deleted with those same tools. VMware administrators can only delete snapshots taken with VMware tools.

   To delete a VM snapshot from the Web Client Host and Clusters or VMs and Templates view, select the target VM and click the Snapshots tab in the adjacent pane to display a list of its snapshots.

   Select the snapshot to be deleted, click the All Actions button, and select Delete Snapshot from the dropdown menu to launch the Confirm Delete wizard. Click Yes to confirm the deletion.

   VMware removes the VM’s snapshot files from the vVol datastore and directs the array to destroy the snapshot. Depending on whether FlashArray Safemode is enabled or not will have differing outcomes on the array.

   When Safemode is disabled the VASA Provider will destroy and automatically eradicate the deleted managed snapshot. This helps reduce object count churn in environments that leverage managed snapshots as part of backup workflows.

   One of the options when Safemode is enabled is disabling the manual eradication on the array. This means that the VASA Provider is no longer able to automatically eradicate the deleted managed snapshot. Keep this in mind when planning object count headroom when using vVols with FlashArray Safemode.

   FlashArray GUI View - Deleted Managed Snapshot objects are eradicated
   FlashArray GUI View - Safemode is enabled - Deleted Managed Snapshot objects are not eradicated

   When VMware deletes a conventional VM snapshot, it reconsolidates (overwrites the VM’s original VMDKs with the data from the delta VMDKs). Depending on the amount of data changed after the snapshot, this can take a long time and have significant performance impact. With FlashArray based snapshots of vVols, however, there is no reconsolidation. Destroying a Flasharray snapshot is essentially instantaneous. Any storage reclamation occurs after the fact during the normal course of the array’s periodic background garbage collection (GC).