Back in the old days, last week, Azure virtual machines had a maximum OS drive size of 127 GB. This worked fine if you were deploying virtual machines from the Azure Marketplace, but was less useful if you were trying to migrate a physical PC or virtual machine from on-premises which had a larger OS drive.
I’m pleased to announce the maximum OS drive has been increased by a factor of 8 to 1023 GB. Last week, a new update rolled out globally to remove the 127 GB limit which applies to both Windows and Linux VMs. All public regions have been updated and the China and Government clouds will also follow suit soon.
Though the limit has been increased, it’s not recommended to use the OS drive for performance intensive production workloads. Disk caching is optimized for OS performance, and for applications with persistent data requirements you can get better throughput by using an attached data drive. The guidance remains the same, but the 127 GB maximum size is no longer enforced – opening up simpler and more straightforward VM migration into Azure, particularly where on-premises apps and data reside on the OS drive beyond 127 GB.
There is also no change in recommendations for applications running on Azure VMs with more demanding IO requirements. If you need maximum IO performance and require disk persistence across hardware failure and reboots, you have the option of using Premium Storage currently in preview, which with disk striping, can provide up to 50,000 IOPS per VM. Performance intensive applications which do not need to be backed by the Azure Storage Service (i.e. don’t need to keep their data across reboots and hardware failure events) also have the option of using SSD temp drives with D Series VM sizes.
Note that there are no plans to increase the OS drive sizes for VM images in the Azure Gallery/Marketplace, or for VMs you’ve already deployed. The OS drive limit increase is for migrating VHDs from on-premises.
Now that the 127 GB OS drive limit has been octupled, we’ll be updating the existing documentation and introducing updates to our Azure DR and migration offerings to reflect the new 1023 GB limit.