If you have a need to restore just a single disk of a multi-disk virtual machine and you perform a normal restore, after the restore will be done the restored VM is configured with just the restored disk(s) and the rest of the disks are missing.
When restoring a single disk to and overwriting a VM the VM is reconfigured and the VM disks that are not restored are disconnected from the VM.
Please follow these steps to restore a single disk of a multi disk VM on a ESX host, when the ESX host is credentialed. If the ESX host is not credentialed please see the following KB https://support.quest.com/Search/SolutionDetail.aspx?id=SOL90084.
1. For the VM disk(s) that you do not need to restore select Skip this Disk option from the dropdown next to the disk when creating a restore job.
2. For the VM disk(s) that you do need to restore select a datastore from the dropdown next to the disk, these disks should already have the currently used datastore selected.
Note the same datastore that the VM currently resides needs to be selected for the disk(s) that will be restored.
4. Complete the restore job and run the restore job.
5. During the restore job the VM well be reconfigured and the disks that are not being restored will be disconnected from the VM and when the restore job is complete the VM will have a disk or disks missing. On the restored VM, select "Edit Settings", "Add," then select "Hard Disk." Click Next. Select "Use an existing virtual disk" and click next. Click the Browse button and locate the disconnected disk in the VM directory and click OK. Select the proper Virtual Device Node for the disk. If you are replacing the OS disk, this is probably SCSI (0:1), by default the most of the time the correct Virtual Device Node will be used. Click Next and the Finish.
Note for a ESX COS based restore the disk(s) are just disconnected and the data is not lost.
Note this will have to be done for each disk separately if working with more than one disk.
6. Boot the original VM.