W2008 R2 Hyper-V Hot-Add Storage

One of the features not being talked about too much in Windows Server 2008 R2 Hyper-V is the ability to add new storage.  What does this mean?  It means you can add new virtual hard disks (VHD’s) to a VM while it is running.   It does not mean you can resize a VHD while the VM is running.

Before we go forward, we need to cover some theory.  There are two types of controller in Hyper-V:

  • IDE: The VM must boot from an IDE controller.  You can have 2 virtual IDE controllers per VM and a total of 4 IDE devices attached per VM.
  • SCSI: You cannot boot from a SCSI controller.  You can have up to 4 SCSI controllers, each with 64 attached VHD’s for a total of 256 SCSI VHD’s per VM.

Now don’t panic!  Forget the VMware marketing often done by uninformed shills.  When you install your enlightenments or integration components (IC’s) you’ll get the same performance out of IDE as you will with SCSI.  The only time when SCSI is faster than IDE in Hyper-V is if you don’t or can’t install the enlightenments or IC’s.  That’s because IDE requires more context switches in that scenario.

I normally use a single IDE disk for the operating system and programs.  I then use at least 1 SCSI disk for data.  And here’s why.


With Windows Server 2008 R2 Hyper-V you can add additional SCSI VHD’s to a VM while it’s still running.  You can see the VM configuration above (from VMM 2008 R2).  Adding another disk is easy.  You can see on the top bar that the option to add all types of hardware is greyed out – except for disk.

imageI’ve clicked on disk to reveal the above panel on the right hand side.  I can configure the disk, e.g. select the next available channel, choose a disk type (use existing, pass through, dynamic or fixed), set the size and name the VHD file.  Once I click on OK the disk is created and then made available to the VM.

From then on in, all you have to do in the OS is what you normally would do if you added a hot-add disk.

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