Azure makes it possible to store data on shared SSDs using the DS- and GS-Series virtual machines. This premium storage offers higher IOPS, lower latency, and better service performance for those services that truly require and are able to afford it. Azure Premium Storage is the kind of storage account that makes this possible. This post will explain what Azure Premium Storage can offer you.
Understanding Premium Storage
Normally in Azure, we deploy virtual machines on standard storage, which is based on traditional spinning disks (HDDs). Depending on the machine type, you might get up to 300 IOPS (Basic A-Series) or up to 500 IOPS (all other virtual machines on standard storage) per data disk. If you require more IOPS, you can deploy more data disks and aggregate them to sum up their potential storage. But if you need more IOPS, and you require lower latency, then you should consider deploying Premium Storage, which is based on SSDs.
Once you have deployed a premium storage account, you can create DS- or GS-Series virtual machines that can use SSD data disks. Note that:
- Only these kinds of VMs can use Premium Storage data disks
- These virtual machines can also use standard series data disks — not all of your storage might require fast performance.
Normally when I talk about Premium Storage, I’m talking about data disks, but you can choose the DS-Series to deploy virtual machines with their OS disk on Premium Storage or Standard Storage.
Sizes and Scalability
There are two considerations:
- The size of the data disk
- The scalability of the storage account
The size of your premium storage data disk dictates the performance of the disk. You can deploy premium storage disks of any size, up to 1 TB, but the size is rounded up to determine the performance profile.
If you deployed a 50 GB data disk on premium storage, then it is rounded up to the P10 size and can achieve up to 500 IOPS with a throughput of 100 MB per second.
As with standard data disks, 1 TB is the maximum data disk size. You can exceed this size and aggregate performance by deploying multiple data disks in a virtual machine, and using features of the guest OS to stipe or mirror the data volumes.
A single premium storage account can scale up to 35 TB. If you need more than 35 TB, then deploy data disks from more than one premium storage account.
Virtual Machine Limitations
Look at the above table and pay attention to the throughput of each data disk size. A P10 can push 100 MB per second. Now look at the performance of the DS- and GS-Series virtual machines. Note how the DS-2 spec can only push data at 64 MB per second. That’s like putting a very fast SSD into an old laptop that cannot perform at the same rate as the flash storage.
Notes on Azure Premium Storage
There are a number of things to be aware of when considering premium storage:
- Availability: Premium Storage is only available in some regions. Check here for local availability.
- Conversion: You cannot use an existing standard storage account, and you cannot convert an existing virtual machine to use premium storage.
- Data types: Premium storage accounts only support virtual hard disks.
- Resiliency: SSD data disk storage only offers LRS resiliency option. You’ll have to go with Standard Storage if you require geo-resiliency (GRS).
- Caching: Data disks are configured with read-only caching by default, which satisfies the best practices of most databases, including SQL Server. OS disks stored on Premium Storage are configured with read-write caching.
- Storage Spaces: If you use Storage Spaces to aggregate disks, then configure each virtual disk with one column per data disk — you will need to use PowerShell if there will be more than eight disks/columns.
- Mixed Cloud Services: A Premium Storage-connected virtual machine can be on the same network as Standard Storage virtual machines, but Microsoft recommends not mixing the virtual machine types in the same cloud service — this really only affects Internet end points. Create a DS-Series cloud service and a GS-cloud service.
This is Premium Storage
You should not be considering Premium Storage for honest Sam’s Car Sales because they want a fast SQL Server. Premium Storage is expensive, so the decision to deploy a DS- or a GS- virtual machine with flash-based data disks should be the result of a calculation, and not based on how cold your finger is when you wet it and hold it in the wind.