The original Virtual Hard Disk (VHD) format dates back to the Virtual PC era and was later adopted by early Hyper‑V releases. It supports fixed‑size or dynamically expanding disks up to 2 TB. Thanks to its age, almost every virtualization tool and legacy Windows release understands VHD—but when you push beyond a couple of terabytes or demand high I/O throughput, its limitations become apparent.
Microsoft introduced VHDX in Windows Server 2012 to overcome VHD’s size and resiliency constraints. By redesigning the on‑disk structure, VHDX raises the maximum disk size to 64 TB, adds logging of metadata updates for crash resilience, and checks alignment boundaries for modern storage media. These improvements translate into fewer corruption risks and better performance on large or I/O‑intensive virtual machines.
Key Differences at a Glance
Maximum Size
VHD is capped at 2 TB, whereas VHDX expands that ceiling up to 64 TB. If your VM needs massive data volumes or log storage, VHDX avoids the workarounds you’d need with multiple smaller VHD files.
Performance Enhancements
VHDX lets you choose larger logical sector sizes (4 KB, 16 KB, or higher), reducing overhead when handling big sequential I/O. VHD is stuck with its original sector configuration, so it cannot scale I/O efficiency in the same way.
Crash‑Resilient Metadata
When you modify a VHDX file’s metadata, Hyper‑V first writes a log record, then applies the change. If the host loses power mid‑update, the format uses that log to roll back safely. VHD has no such journal, so a sudden crash can leave the disk header in an inconsistent state.
Online Resize and Alignment Checks
You can grow a VHDX file while the VM is running—no downtime required—and the format enforces 4 KB alignment by default, which is ideal for SSDs and SANs. Although VHD can expand dynamically, it doesn’t offer the same level of safe online resizing or strict alignment verification.
Compatibility Considerations
If you need to move disks between older Hyper‑V, Virtual PC, or third‑party tools, VHD remains the most universally supported option. But in any environment running Windows Server 2012 or later—especially where you care about scale, performance, and data integrity—VHDX is the clear choice.
For more in‑depth guidance and examples, see the official comparison article:
https://www.vinchin.com/vm-tips/vhd-vs-vhdx.html
