Windows Server 8 introduces a new virtual disk format, VHDX. VHDX is an expanded set of features from the traditional VHD file format used in Hyper-V and Xen virtualization environments. The other mainstream virtual disk file formats are VMDK for VMware and VDI for VirtualBox platforms.

The size of up to 16TB is the eye-catching statistic. WOW! That’s huge. This is very, very welcome in times where we will be poised to move more and more tier 1 applications to virtualization platforms. While memory, processor, and network resources aren’t too difficult to manage for large VMs, disk resources can be a challenge. The 2TB limitations for virtual disk files fits most systems, but we have to tweak applications when we go above that range. Now, to be clear; working with ultra-large VMs is not really fun. But, it is a necessary evil today it seems.

The VHDX format also brings a metadata structure aimed at reducing data corruption and improved alignment on large sector disks. More features of VHDX include:

  • Larger block sizes for dynamic and differential disks, which allows these disks to attune to the needs of the workload.
  • 4-KB logical sector virtual disk that allows for increased performance when used by applications and workloads that are designed for 4-KB sectors.
  • The ability to store custom metadata about the file that the user might want to record, such as operating system version, or patches applied.
  • Efficiency (called trim) in representing data, resulting in smaller files size and allowing the underlying physical storage device to reclaim unused space.

Note: the above bullet points are reproduced from the Windows Server 8 Reviewers Guide with permission.

Figure A

Creating a VHDX file (click to enlarge)

Does having a single virtual disk file being able to scale above 2TB appeal to you? Share your comments below.