Just finished my Veeam Technical certification online as a part of the “Veeam University”. I was reminded of the issues with presenting an iSCSI VMware LUN to a Windows based server, which is something that is second nature for me now, but I still see it as quite a trap for those starting off with products like those offered by Veeam.

Veeam Backup and Recovery can backup data from VMware by presenting VMware LUNS to a Windows based server using iSCSI. This is preferable to backing up via the network (which passes all traffic from the SAN through the ESXi host), simply due to the speed that can be achieved with Direct SAN access. The problem with this, is that when you present a disk to a Windows operating system, the disk is automatically mounted and a signature is written to the disk. To avoid Windows corrupting the vmfs partition we need to open a command prompt and disable auto mounting of all disks. This can be done with the diskpart command line utility as shown below :

C:\Documents and Settings\Administrator>diskpart
DISKPART> automount disable
Automatic mounting of new volumes disabled.

Good news is that Veeam Backup and Replication v5 will automatically run the automount disable command as a part of the installation process.

Be aware that installing updates that can affect diskpart, such as Service Packs, may cause the automount feature to revert to being enabled and should be checked as a part of your regular maintenance plan.