Change the Azure IaaS Scratch Drive Letter

Q: Is it possible to change the drive letter from D: that Windows Azure IaaS virtual machines use for the scratch drive and pagefile?

A: When you create a virtual machine in Windows Azure IaaS, in addition to the operating system drive that's stored in Windows Azure Storage, an additional virtual disk is attached. This disk uses scratch drive local storage to the host, which by default includes the operating system pagefile. Because this scratch disk isn't on Windows Azure Storage but is instead on local storage, there are no guarantees about the persistence of the data. Therefore, this disk should be used only for data that can be lost. This drive is D: by default.

Some applications might want to use the D: drive for their own purposes. To change the drive letter used by the scratch drive use RDP to create a remote session to the Windows Azure virtual machine.

You need to temporarily move the pagefile from D: in order to change the drive letter. Open the Control Panel System applet and select Advanced system settings. On the Advanced tab, select Settings in the Performance area. Click the Advanced tab, and select Change in the Virtual memory area. Set the pagefile size on D: to No paging file, and select System managed size on C:. Make sure you click Set, then OK. Restart the virtual machine.

After the virtual machine restarts, the pagefile will be on the C: drive. Launch Disk Manager (diskmgmt.msc) and change the drive letter from D: to another letter such as S:.

You now need to move the pagefile to the new drive letter for the scratch disk. Repeat the process that you initially used to move the pagefile, but this time set C: to No paging file and select System managed size on S: (or whatever letter you used). Click Set, then OK.

After you reboot the virtual machine, you'll be able to add data disks to the virtual machine and give one of them the D: drive letter.