Each VM has one; it is a managed disk with the operating system on it (C: under Windows) and is kept when the VM is resized or redeployed.
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In the Ultra Transcenders books
Each book explains OS disk in context, with comparison tables and the common traps.
Terms in this definition
- OS
Operating system, which you manage yourself on IaaS VMs. PaaS offerings like App Service do not expose it.
Related terms
- Confidential disk encryption
Available just for confidential VMs, this encrypts the OS disk with keys bound to that VM's TPM, meaning the disk is unreadable anywhere else.
- Ephemeral OS disk
An OS disk held on the VM host's local storage instead of Azure Storage. It keeps no state across redeploys or resizes, can't be stopped and deallocated, and isn't supported by Azure Backup, Site Recovery or ADE.
- Redeploy
VM operation that relocates the machine to another host in Azure, keeping its OS disk, data disks and configuration while wiping whatever is on the temporary disk.
- vTPM
A virtualised Trusted Platform Module within a VM. On confidential VMs, the OS disk keys are bound to it by confidential disk encryption.