HotAdd Transport mode limitations with vSAN datastore

Products

• VMware vSphere ESXi

Issue/Introduction

VDDK has 3 backup modes available:

• SAN
• HotAdd
• NBD

When using vSAN, there are a few limitations of VDDK backup using HotAdd transport mode with vSAN datastores.

Environment

VMware vSphere 6.5.x
VMware vSphere 6.7.x

Cause

The default behavior should be HotAdd. This can be achieved when the proxyVM and the target VM both reside on vSAN. If the proxy VM or the target VM either entirely or partially reside on a mix of other storage (VMFS or NFS), then there are limitations that require setting the backup mode to NBD.

Resolution

Below are the limitations that require setting the backup transport mode to NBD:

• Cross filesystem type:
  
  When the target machine has a vSAN datastore and the backup proxy resides on a non-vSAN datastore, HotAdd backup is not supported. There is no workaround. This limitation goes back to vSphere 6.5 and has not been fixed by vSphere 8.0.
  
  
• SEsparse snapshot issue:
  
  When the target machine has a VMFS or NFS datastore and backup proxy resides on a vSAN datastore, HotAdd backup is not supported when there were SEsparse disks. This issue existed in vSphere 6.x but was fixed in VDDK 7.0 for vSphere 7.0.

Additional Information

Information about SEsparse snapshots:

• On a VMFS 6 datastore, disk snapshots are created in SEsparse format.
  
  
• On a VMFS 5 or NFS datastore, disks snapshots are created in SEsparse format, and SEsparse format is used for disks larger than 2TB.

Virtual Disk Transport Methods