I use iSCSI LUNs and Windows Server Backup to back up my virtual machines. So far that has worked ok, but sometimes when a server reboots it will map the iSCSI LUN but fail to bring the disk online. Of course this leads to backups failing:

And as it turns out, the backup disk is indeed offline:

Using diskpart, the commands to rectify this would now be:

select disk 1
online disk

But of course I don’t want to do that manually, and besides it’s not always “disk 1”. Some PowerShell should however fix this.

Using the “Win32_DiskDrive” WMI Class I can display information about the physical disks in my machine:

All my iSCSI LUNs are being mapped from a Synology NAS, so I’ll use the model name property to narrow down the selection. The property I need for diskpart is “index”:

An example of a system with multiple iSCSI LUNs:

The script will do a “foreach” through all drives matching the filter criteria, build a diskpart command batch and pipe it to diskpart.exe:

$iSCSI = gwmi win32_diskdrive | where {$_.model -like "synology*"}
foreach ($disk in $iSCSI) 
{ 
$diskID = $disk.index
$dpscript = @"
select disk $diskID
online disk noerr
"@
$dpscript | diskpart
}

The result:

If the disk was already online the script will just continue with the next disk, courtesy of the “noerr” parameter in the diskpart batch.