Data Domain Virtual Edition running on Azure has system disk which is not for the operating system or NVRAM

Data Domain Virtual Edition (DDVE) running on Microsoft Azure requires the following storage to work (note details may change in later DDOS versions):

• One 250 GiB Standard HDD or Premium SSD root disk, for the DDVE and DDOS operating system
• One 10 GiB Standard HDD or Premium SSD NVRAM disk
• As many as necessary 1 TiB or 2 TiB Standard HDD or Premium SSD for local backup metadata

However, when looking into the DDVE storage details from the CLI or the UI, users may notice the presence of an additional disk which is not the operating system, the NVRAM, or any of the local metadata disks they have added. For example:

Disk   Slot        Manufacturer/Model         Firmware   Serial No.   Capacity    Type
       (pci/idx)
----   ---------   ------------------------   --------   ----------   ---------   ----
dev1   2:0         Msft    Virtual_Disk       n/a        (unknown)    250.0 GiB   SAS  <<-- OS disk
dev2   3:0         Msft    Virtual_Disk       n/a        (unknown)    600.0 GiB   SAS  <<-- Azure disk
dev3   1:0         Msft    Virtual_Disk       n/a        (unknown)    10.0 GiB    SAS  <<-- NVRAM disk
dev4   1:1         Msft    Virtual_Disk       n/a        (unknown)    1.0 TiB     SAS  <<-- Metadata disk #1
dev5   1:2         Msft    Virtual_Disk       n/a        (unknown)    1.0 TiB     SAS  <<-- Metadata disk #2
dev6   1:3         Msft    Virtual_Disk       n/a        (unknown)    1.0 TiB     SAS  <<-- Metadata disk #3
----   ---------   ------------------------   --------   ----------   ---------   ----

In the above instance, the DDVE does not use the 600.0 GiB disk. It is not for the operating system, the NVRAM, or storage for local metadata backups.

Azure adds this disk when creating a new VM. For most of the VM types, Azure has on offer, including the VM types used when deploying DDVE from the marketplace.

For example, for DDOS 7.11, if creating a DDVE with up to 96 TiB storage capacity, a "Standard_D16ds_v5" type of Azure VM is used for deployment. Details of storage requirements are found in the "Dell PowerProtect DDVE in the Azure Cloud 7.11 Installation and Administration Guide." Shown below for reference is the table from the guide which outlines the VM resources:
 
As shown in the table above, for the VM type used for installing DDVE, Azure adds a "Temp storage (SSD)" of 600 GiB to the DDVE VM, even if DDVE does not have any use for it.
 

From the Microsoft Azure documentation:

   Temporary disk

   Most VMs contain a temporary disk, which is not a managed disk.

   The temporary disk provides short-term storage for applications and processes, and is intended to only store data such as page files, swap files, or SQL Server tempdb.

   Data on the temporary disk may be lost during a maintenance event or when you redeploy a VM. 

   During a successful standard reboot of the VM, data on the temporary disk will persist.

   For more information about VMs without temporary disks, see Azure VM sizes with no local temporary disk.

There is no action required on the Data Domain DDVE side. The additional disk can be ignored. It is not being used by DDOS at all.

The disk is added as an integral part of the Azure VM type used by DDVE, and should not be modified, altered, or deleted.

The Microsoft Azure cloud provider does this itself and hence, if there are doubts, we recommend contacting Microsoft Azure support for more details.