Looking to enhance virtualisation performance under Hyper-V? Centralise storage and shift to VHDX.
The VHDX format for virtual machine images was introduced as part of Windows Server 2012, succeeding the earlier (and still supported) VHD format. Microsoft now recommends it as the default for any new virtual machine (VM) rollouts.
“VHDX is the default virtual disk format,” Hyper-V group program manager Mathew John explained during a presentation at TechEd North America 2013. “We created VHDX because we realised VHD with its limits of 2TB was not sufficient. We wanted a format that was simple but more resilient. VHD works, it’s great, but the future is VHDX. We have to keep moving the world forward.”
Benefits of VHDX, apart from its maximum 64TB size, include larger block sizes and the ability to embed custom metadata. However, one of the most evident advantages is improved performance, which Johns and performance engineer Liang Yang demonstrated in a series of tests. One demonstration of allocating blocks from scratch showed a tenfold performance improvement for VHDX. In typical activities, performance is around twice as good,
VHDX also allows on-the-fly resizing of VMs, with the ability to make them both larger and smaller. “Shrink is a safe operation; if you have data in a VM we won’t shrink beyond it,” John saod.
John recommends adopting centralised storage for larger virtualisation deployments. “If it’s a fairly small 1-host or 2-host deployment, maybe you’re OK with having local disk, but for any largish deployment, centralised disk is what works for economy and performance,” he said. “So decouple your storage and compute. You’ll also have a better handle on what kind of resource you’re allocating to your virtual VM.”