Hyper-V Storage Types

Hyper-V Disk Storage Types :

                          For data storage, virtual machines use either a virtual hard disk (VHD) or a physical disk that is directly attached to a virtual machine (also known as a ―pass-through‖ disk). You can easily configure virtual machines to use either a fixed-sized VHD or a dynamically expanding VHD, or to directly access a physical disk. All virtual machines access virtual storage using virtual storage controllers, specifically a virtual IDE or SCSI controller.

Virtual Hard Disk Architecture:

                         A .vhd file is created on a host volume and exposed as a virtual hard disk to the virtual machines. The .vhd file functions as a set of disk blocks and is stored as a regular file using the NTFS file system. There are three types of VHDs: fixed-size, dynamically expanding, and differencing.

Storage Type: Fixed-size VHD

1. A fixed-size VHD is a file stored in an NTFS partition that uses the full amount of space specified when the VHD was created.
2. A fixed-sized VHD performs slightly better than a dynamically expanding VHD because the VHD file is initialized at its maximum size when it is created on a physical hard drive.
3. You can always increase the size of a fixed-size VHD using Hyper-V Manager or by running a Windows PowerShell script.
4. Maximum size of a fixed-size VHD = 2040 GB

Storage Type: Dynamically Expanding VHD

1. A dynamically expanding VHD is a file stored on an NTFS partition that grows in size each time data is added. It provides an efficient use of available storage.
2. You can compact a dynamically expanding VHD, which reduces the size of the .vhd file by removing unused space left behind when data is deleted from the VHD.
3. Maximum size of a dynamically expanding VHD = 2040 GB
 

Storage Type: Differencing VHD

1. A differencing VHD is a special type of VHD that stores changes to an associated parent VHD for the purpose of keeping the parent VHD intact. Changes continue to accumulate in the differencing VHD until it is merged to the parent disk.
2. The parent VHD of a differencing VHD can either be a fixed-size VHD, a dynamically expanding VHD, or a differencing VHD (differencing chain).

Storage Type: Physical Disk

1. Disk storage can be configured as a physical disk directly attached to a virtual machine. In addition, disk storage can be configured as a storage area network (SAN) LUN attached to a virtual machine. These disks are also known as ―pass-through‖ disks.
2. From the management operating system perspective, the disk is in an offline state, which means direct read and write access to the disk is not available.
3. These disks do not support dynamically expanding VHD, differencing VHD, or virtual machine snapshots.
4. These disks are not limited to 2040 GB in size.