Q: I ran out of physical disk space in my Storage Pool and now my virtual disks are offline--how can I get access to the data?

A. If you're using thin provisioning of virtual disks in your Storage Pool and the Storage Pool has run out of available space (you would have been getting warnings at 70 percent full) then you need to add more disks to the pool.

The reason the virtual disks (and the entire Storage Space) have gone offline is to protect the disks from risk of corruption as a result of write actions failing due to no available underlying storage.

After you add more disks, you will be able to bring the Storage Space back online. If you don't have more disks available, but need to access the existing data, you can bring the Storage Space online in a read-only mode (replace with the actual friendly name of your virtual disk):

Get-VirtualDisk -FriendlyName | Get-Disk | Set-Disk -IsReadOnly $true
Get-VirtualDisk -FriendlyName | Get-Disk | Set-Disk -IsOffline $false

Once you resolve the problem by adding more storage you will need to set it back to read-write:
 

Get-VirtualDisk -FriendlyName | Get-Disk | Set-Disk -IsOffline $true
Get-VirtualDisk -FriendlyName | Get-Disk | Set-Disk -IsReadOnly $false
Get-VirtualDisk -FriendlyName | Get-Disk | Set-Disk -IsOffline $false