Article number
000003499
Affected Versions
All
Source Hypervisor
All
Target Hypervisor
All

What Is a VRA Helper (also known as a diskbox or shadow VRA)

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Description

 A VRA is a virtual machine installed on each hypervisor host where
VMs are to be protected from or to. The VRA manages the replication of data from protected virtual
machines to the recovery site. The target VRAs are responsible for maintaining any protected VMs.

The VRA-H is a VM created to assist the VRA to hold the recovery disks. Due to a hypervisor limitation, a single VM can hold up to 60 disks, so when the VRA is getting close to that limit, it will create a VRA-H VM and will attach the needed disks to it. 

 

Summary

VMware and Microsoft impose a limitation of 15 SCSI targets per SCSI controller and 4 SCSI controllers per virtual machine. This amounts to a limitation of 60 SCSI targets per virtual machine. VRAs, which serve as hosts for replica volumes, may require access to SCSI targets beyond this limit. Zerto Virtual Replication uses a VRA helper to get around this limitation.

 

When working with Zerto Virtual Replication, an administrator may notice a new VM, labeled "Z-VRAH" followed by a string of numbers\ host name, listed in their datacenter/Fabric.  What is this VM and what does it do?

Steps

What is a Helper VRA?
  • A VRA Helper is a VM linked to a VRA, which provides additional available SCSI targets.  
  • A VRA Helper does not have an OS and therefore does not have an IP address or use VMware tools.
  • A VRA Helper is created proactively at the target site and prior to the target VRA reaching the SCSI target limit. Normally, once a VRA or a Helper reaches 50 attached volumes, the ZVM will create and deploy a new VRA helper.
  • Similar to a VRA, a VRA Helper must be left to Zerto Virtual Replication to manage, and must not be modified for any reason.