Introducing SSD storage account support for Ephemeral OS disks

We are excited to announce the Public Preview of SSD storage account support during creation of VM/VMSS with Ephemeral OS Disk. By utilizing SSD with Ephemeral OS disk, customers can benefit from the following enhancements:

• Enhanced SLA: VMs created with Premium SSD provide the maximum 99.9% SLA, while VMs created with Standard HDD provide 95% SLA. Customers can enhance SLA to 99.9% for their VMs by choosing Premium SSD as base disk.
• Improved performance: By choosing Premium SSD as the base disk, customers can enhance the disk read performance of their VMs. While most writes occur on the local temp disk, some reads are performed from managed disks. Premium SSD disks provide 8-10 times higher IOPS than Standard HDD. (For details, refer Select a disk type for Azure IaaS VMs - managed disks - Azure Virtual Machines | Microsoft Learn).

Ephemeral OS disks are split into 2 disks - a diff disk on local temp disk and a base disk using managed disks. All writes to existing and new files occur on the diff disk, while the original files are read from the base disk. Both the diff disk and the base disk are crucial for the VM's operation.

SSD support is a new option that allows customers to choose the type of base disk that is used for the ephemeral OS disk. Previously, the base disk could only be Standard HDD. Now, customers can choose between the three types of disks: Standard HDD(Standard_LRS), Standard SSD (StandardSSD_LRS) or Premium SSD (Premium_LRS). By using SSD as the base disk, customers will achieve higher SLA and better performance compared to Standard HDD. Standard HDD as base disk will continue to be free to use with Ephemeral OS disk. However, customers will incur additional disk cost for provisioning SSD as the base disk.

How to use SSD with Ephemeral OS disk?

To utilize SSD with Ephemeral OS disk, customers need to specify the disk type when creating or updating a VM with an ephemeral OS disk enabled. Customers can use the Azure CLI, Azure PowerShell, or Azure Resource Manager templates to achieve this.

For example, to create a VM with Ephemeral OS disk & Premium SSD base disk, customers can use the following command:

AzCLI

az vm create --name MyVM --resource-group MyRG --image UbuntuLTS --ephemeral-os-disk true --storage-sku Premium_LRS

PowerShell

Set-AzVMOSDisk -VM $VirtualMachine -DiffDiskSetting Local -DiffDiskPlacement ResourceDisk -CreateOption FromImage  -Caching ReadOnly -StorageAccountType "Premium_LRS"

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