VMware Vsphere

  • What it backs up: This option allows you to create backups of your virtual machines running on VMware vSphere, including vCenter Server and ESXi hosts.

  • Benefits:

    • Live Backups: Virtual machines can be backed up without taking them offline, minimizing downtime and disruption.

    • Efficient Backups: This method uses Changed Block Tracking (CBT) technology (when available) to only transfer changed data, improving backup speed and storage efficiency.

  • Backup Process Breakdown: This method backs up your VMware virtual machines without needing them to be offline. Here's how it works: A temporary snapshot of the virtual machine is captured to ensure a complete copy at the backup time. Only the necessary files, like configuration and virtual disks, are transferred for backup, using a chunking process for efficiency. Once the transfer is complete, the temporary snapshot is released, freeing up resources on the virtual machine.


  • Local Deployment: For peak performance, deploy Zmanda Pro as a VM on the same ESXi cluster or host it's backing up. This minimizes network traffic when transferring large disk image files.

  • Parallel Processing: Zmanda Pro allows you to choose how many VMs are backed up concurrently. Strategically selecting this value can significantly speed up backups.

  • Changed Block Tracking (CBT): Leverage CBT to streamline backups. It identifies and reads only data blocks modified since the last successful backup, reducing data transfer and accelerating backups. Both standard and CBT backups skip unallocated disk areas for further optimization.

  • NBDSSL with FastLZ Compression: When using CBT, Zmanda Pro utilizes the secure NBDSSL protocol for data transfer. Additionally, it employs fastlz compression within NBDSSL to shrink data size on-the-fly, minimizing network traffic and speeding up backups.


  • Desktop Client: Windows x86_64 only, running on the same network as the target ESXi/vCenter.

  • Server: vSphere 6.7 (ESXi or vCenter) or later.

Required Roles

In Zmanda Pro, roles determine what actions users are allowed to perform.

  • Global: Enable/disable methods,

  • Datastore: allocate datastore space, browse datastore, perform low-level file operations. Users with the capability to Allocate Datastore Space can reserve and allocate storage within the datastore, ensuring adequate capacity for tasks or purposes. They can also Browse Datastore, navigating its contents to view and access files and folders. Additionally, they have the authority to Perform Low-Level File Operations, enabling tasks like file management and manipulation directly on the datastore, beneficial for granular file management on the ESXi host.

  • Virtual Machine: Provisioning, allow read-only disk access, allow virtual machine download.

  • Snapshot management(ESXi state): create/remove snapshots. Users with this capability can create new snapshots to capture the current state of virtual machines or remove existing snapshots as needed, providing a mechanism for data protection and recovery.

Protected Item configuration (desktop client)

  1. From the list of protected items, choose "VMware vSphere".

  2. Under "Connection," choose "vSphere API" and click "Configure..."

  3. Enter valid vCenter/ESXi credentials with the required roles set (refer to "vSphere Connection" details for specific roles).

  4. Use "Test Connection" to verify connectivity.

  5. Click the "+" sign to select VMs. Choose "VMware vSphere" to back up all VMs, or select individual VMs.

  6. Select the desired backup type for the chosen VMs (refer to "Options" for available modes).


  • vSphere Connection: Zmanda Pro leverages the vSphere SOAP API (VADP) for communication with the vSphere server. Data transfer from the datastore utilizes the NBDSSL protocol.

  • Setting Details Server: This section allows specifying the vCenter/ESXi host (including custom ports) and an optional thumbprint for enhanced security through SSL certificate validation. Username and password are required for authentication.

  • Options:

    • Latest VM state (Changed Block Tracking): This recommended option provides optimal performance by backing up only modified disk sectors since the last successful backup.

    • Latest VM state (Standard): This option backs up the current state of all disks and VM configurations, flattening past snapshots into a single disk with the latest state.


For both Changed Block Tracking and Standard mode:

  • Performance is optimized by skipping over unallocated disk sectors.

  • Data transfer occurs over the NBDSSL protocol.

  • Separate snapshot files are not included in the backup; the current VM state is flattened into a single disk image.

  • Independent disk mode on disks is not supported and will cause the backup process to skip them.


While Zmanda Pro can restore individual files and folders for NTFS partitions, recovering an entire VM requires a multi-step process. Here's an overview:

  1. File Restoration: Zmanda Pro restores the VM configuration file (.vmx) and virtual disk files (.vmdk) to your local disk.

  2. Manual Transfer: You'll then need to manually copy these restored files to the appropriate ESXi datastore using your preferred data transfer method.

  3. VM Import: Finally, utilize the ESXi/vCenter interface to import the recovered VM. This process essentially re-registers the VM with the ESXi host, making it accessible again.

The disk that is restored will be a compressed copy of the snapshot branches if your backup was made while a virtual machine was operating off of a snapshot. To correctly re-import this virtual machine:

  1. Update the VMX configuration with "scsi0:N.fileName = <file>".

  2. Optionally, reclaim disk space using "vmkfstools -K <vmdk>" to optimize backup performance.

  3. If Changed Block Tracking (CBT) was enabled, it's recommended to disable or restart CBT before the first boot.

Granular Restore: For NTFS partitions, you have the option for granular restoration of single files and folders.


Enabling Detailed Logging:

If encountering difficulties during restore operations, Zmanda Pro offers diagnostic logging to gain deeper insights into the process. You can enable debug logging for a specific backup job to generate more verbose logs:

  1. Initiate the failed backup job again.

  2. In the storage vault selection, select "Show advanced options."

  3. Locate "Log Level" and change it from "Default" to "Debug."

  4. Initiate the backup once more. The job log will now display more detailed information to assist in troubleshooting.

Enabling CBT inside VMware vSphere

CBT is an optional feature for VMs and disks within VMware vSphere. To leverage CBT mode in Zmanda Pro, you'll need to enable CBT on the target VMs and their disks beforehand. Here's a simplified guide:

  1. Power off the VM.

  2. Access the VMware vSphere web interface and select "Edit" for the desired VM.

  3. Go to the "VM Options" tab in the "Edit Settings" dialog box.

  4. Locate the "General" section and find "Configuration Parameters." Click "Edit configuration."

  5. Set ctkEnabled to TRUE to enable CBT or FALSE to disable it.

  6. Repeat step 5 for each attached disk, setting scsix:x.ctkEnabled accordingly.

  7. If disabling CBT, delete any *-CTK.VMDK files from the VM's directory using the datastore browser.

  8. Power on the VM again.

Common errors and warnings

This section addresses frequently encountered errors and warnings you might experience during VM restore operations with Zmanda Pro. By understanding these messages, you can effectively troubleshoot potential issues and ensure successful recoveries.

CBT and Initial Backup:

  • "No parent snapshot found. Fallback to full backup"

This message indicates that Zmanda Pro couldn't locate a suitable reference backup job for Changed Block Tracking (CBT). This typically happens during two scenarios:

* **First backup in a storage vault:** When performing the initial backup within a new storage vault, there's no prior backup to reference for CBT. As a result, Zmanda Pro automatically defaults to a full backup. The subsequent backup, assuming success, should leverage CBT for increased efficiency.
* **Previous backup failure:** If a previous backup attempt failed, Zmanda Pro might not be able to find a valid reference point for CBT. In this case, the current job will also proceed as a full backup. The next successful backup will then re-establish the CBT baseline and enable future CBT-based backups.

Snapshot Handling:

  • "VM <name> contains <N> snapshots(s). Snapshots will be flattened during backup"

This message informs you that the target VM was running off a snapshot chain during the backup process. Zmanda Pro will create a flattened virtual disk image by merging the current snapshot with its parent(s) up to the base disk. This essentially consolidates the snapshot hierarchy into a single disk for the restored VM. While the snapshot tree structure won't be preserved, the current state of the VM will still be recovered.

Disk Changes and Inconsistencies:

  • "Unable to run CBT: disk size changed <old> -> <new>"

This error signifies that the virtual disk size has changed since the last successful backup using CBT. As CBT relies on tracking block-level modifications, significant disk size alterations render it unusable. Zmanda Pro will automatically switch to a full backup in this scenario.

  • "Unable to run CBT: inconsistent change id <old> -> <new>"

This message indicates that the change ID information for the virtual disk has become inconsistent compared to the last successful CBT backup. Inconsistent change IDs prevent Zmanda Pro from accurately identifying changed blocks. As a result, the current backup job will proceed as a full backup to ensure complete data capture.

Unsupported Disk Configurations:

  • "Unsupported disk mode <mode>"

This error occurs when Zmanda Pro encounters a virtual disk configured with an unsupported independent disk mode (persistent or non-persistent). These disk modes don't support snapshots, which are a vital component of the Zmanda Pro backup process. Consequently, disks with such configurations will be skipped during the backup.

  • "Unsupported disk backing"

This message indicates that Zmanda Pro encountered a virtual disk created using a format it doesn't recognize or support. Disks with unsupported backing formats will be skipped during the backup process.

Permission and Configuration Issues:

  • "Error downloading file: download(<file URL>): 401 Unauthorized"

This error suggests that the credentials used by Zmanda Pro lack the necessary "Datastore" role(s) on the target host or VM. To resolve this, ensure the credentials possess the appropriate permissions to access and download files from the relevant datastore and VM. Refer to the documentation for details on required roles and permissions.

  • "CBT is not enabled on <vm name>"

This message highlights a configuration mismatch. While CBT might be enabled within the Zmanda Pro protected item settings, it's currently disabled on the target VM itself. To leverage CBT for backups, ensure CBT is activated on the target VM within VMware vSphere.

Informational Messages:

  • "Disk chain before snapshot\n<list-of-vmdk>\nNew snapshot file\n<list-of-vmdk>"

This message provides informative details about the virtual disk configuration associated with the VM. It lists the virtual disk chain before a snapshot is taken, followed by the newly created snapshot file. If there are multiple snapshot trees for the VM, this message will also display the specific chain being backed up

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