A disk image format for virtual hard disks; the Azure Migrate appliance for Hyper-V, for instance, is downloaded as one.
Also called virtual hard disk.
Read more: Microsoft Learn
In the Ultra Transcenders books
AZ-305AZ-104AZ-900AZ-802MD-102
Each book explains VHD in context, with comparison tables and the common traps.
Terms in this definition
- FORMAT
A DAX function that turns a value into text according to a format string, for instance "MMMM" to show a month's name. Since the output is text, numeric operations can't use it, and dynamic format strings were introduced to get around that.
- Azure Migrate appliance
Discovery VM run on premises and registered to exactly one Azure Migrate project; it is deployed from a Hyper-V VHD, a VMware OVA or an installer script, finds servers without agents and collects the performance data that assessments draw on.
- Hyper-V
The hypervisor built into Windows. The VMs for the Azure Extended Network appliance require the Hyper-V role, using nested virtualisation, and an external virtual switch for each NIC.
Related terms
- Dynamically expanding disk
A VHD or VHDX that begins small and gets bigger as data is added, until it reaches its configured limit.
- Fixed-size disk
A virtual hard disk that takes up its whole size as soon as it is created, which makes its performance predictable.
- imageReference
A property in a VM's
storageProfilethat identifies a platform or Marketplace image through publisher, offer, sku and version. VHD URIs and custom images are specified through different properties. - Server-side encryption
Encryption at rest that Azure Storage always applies to managed disks, with keys managed by the platform or the customer. Caches and temp disks are excluded, and a VHD you download is unencrypted.
- Unmanaged disks
An older approach, now retired in favour of managed disks, where VM disks were VHD page blobs kept in a storage account you owned.
- VHDX
Allows Hyper-V virtual disks as large as 64 TB and copes better than VHD with corruption caused by power cuts.