Disk partition preservation
This article outlines the different scenarios that affect your Azure virtual machine (VM) instances, and what happens to the different disks on those VMs.
Note
This information applies to stateless platform as a service (PaaS) VMs. It doesn't apply to Azure virtual machine persistent VMs.
Azure disk partitions
The following table describes the contents of the various disk partitions.
| Designation | Use | Description |
|---|---|---|
| C | Local resource disk | This disk contains Azure logs and configuration files, Azure Diagnostics (which includes your Internet Information Services (IIS) logs), and any local storage resources that you define. |
| D | Windows disk | This partition is the operating system (OS) disk. It contains the Program Files folder (which includes installations that are done through startup tasks unless you specify another disk), registry changes, the System32 folder, and .NET Framework. |
| E or F | Application disk | This disk is where your cloud service configuration package (.cspkg) file is extracted to. The disk contains your website, binaries, role host process, startup tasks, web.config file, and so on. |
Disk preservation
The following table shows the different virtual machine processes that might occur, and whether the corresponding disk partitions are preserved or rebuilt for each process.
| Virtual machine process | C (local resource) | D (Windows) | E or F (application) |
|---|---|---|---|
| Virtual machine reboot within the VM* | Preserved | Preserved | Preserved |
| Internal fabric node recovery (power cycle node) | Preserved | Rebuilt | Preserved |
| Portal reboot, host OS update, or stop or start service | Preserved | Preserved | Rebuilt |
| Portal reimage or guest OS update | Preserved | Rebuilt | Rebuilt |
| In-place upgrade (default when deploying from Visual Studio) | Preserved | Preserved | Rebuilt** |
| Node migration (server failure) | Rebuilt | Rebuilt | Rebuilt |
| Rebuild role instance | Rebuilt | Rebuilt | Rebuilt |
* This restart is done from within the virtual machine, such as running the shutdown /r /t 0 command. The portal restart is done by selecting the Reboot button in the Azure portal.
** In this scenario, the application disk will switch from Drive E to F (or F to E). To detect the current application disk, applications should query the %RoleRoot% environment variable.
Contact us for help
If you have questions or need help, create a support request, or ask Azure community support. You can also submit product feedback to Azure feedback community.