A Veeam proxy server is configured as follows. No modifications are allowed to the transport mode. When performing a restore of a VMware virtual disk using this proxy server, the restore fails. What is a possible cause?

The Veeam proxy is configured to use the "Direct storage access" transport mode, also known as Direct SAN. This mode has a specific limitation during restore operations. The vSphere APIs used for Direct SAN access do not support writing to thin-provisioned disks in a way that preserves their thin format. Consequently, when Veeam attempts to restore a thin-provisioned virtual disk using this transport mode, the operation will fail. Veeam can only restore disks as thick-provisioned when using Direct SAN access.

A. CBT is enabled on the virtual disk.

Changed Block Tracking (CBT) is a VMware feature used to accelerate incremental backups, not restores. Its status does not affect the restore transport mode.

B. CBT is disabled on the virtual disk.

Similar to the reason above, the status of Changed Block Tracking (CBT) is irrelevant to the success or failure of a restore operation.

D. The virtual disk is thick-provisioned.

Direct Storage Access mode fully supports restoring thick-provisioned disks. This configuration would result in a successful restore, not a failure.

1. Veeam Backup & Replication V12 User Guide for VMware vSphere

"Direct Storage Access

" section "Restore."

Reference Text: "When you restore a VM disk

Veeam Backup & Replication inflates the disk to the thick format. You cannot restore disks in the thin format in the Direct SAN access mode." This statement directly confirms that attempting to restore a thin-provisioned disk is not supported and is a valid cause for failure.

This guide is the primary official vendor documentation for Veeam Backup & Replication V12.