Understanding Azure disks

Azure disks are block storage primarily intended for virtual machines. They present varying levels of performance on Azure depending on your requirements and choice of stock keeping unit (SKU).

Disk management options

Azure disks come with two management options:

• Managed disks: Azure takes care of the management of the disks for you. The platform automatically manages where the disk is stored, how it scales, and that it delivers at the intended performance. Managed disks also come with higher Service Level Agreement (SLAs) than unmanaged disks. Disk costs are calculated at the size of the provisioned disk regardless of the data consumed. Managed disks are recommended by Microsoft over unmanaged disks.

• Unmanaged disks: These disks are managed by you. This requires the allocation of the disk to a storage account. The management of the allocation of disks to storage accounts is vital to ensure the reliability of the disks. Factors such as storage space available on the storage account, and storage account type are pivotal for managing these disk types. Disk costs are calculated based on consumed data on the disk.

Disk performance

When selecting the correct disk for your application’s purpose, consider the reliability and performance requirements. Factors that should be considered include the following:

• IOPS: IOPS (input/output operations per second) refers to a performance measurement for storage that describes the count of operations performed per second.

• Throughput: Disk throughput describes the speed at which data can be transferred through a disk. Throughput is calculated as IOPS x I/O Size = Disk Throughput.

• Reliability: Azure offers better SLAs based on the disk type chosen in conjunction with a VM.

• Latency: Latency refers to the length of time it takes for a disk to process a request received and send a response. It will limit the effective performance of disks and therefore it’s pertinent to use disks with lower latency for high-performance workloads. The effect of latency on a disk can be expressed through the following example. If a disk can offer 2,500 IOPs as the maximum performance but has 10 ms latency, it will only be able to deliver 250 IOPs, which will potentially be highly restrictive.
• Premium storage provides consistently lower latency than other Azure storage and is advised when considering high-performance workloads.

Top Tip

Azure VM SLAs on a single instance that have premium SSD disks attached go up to 99.9% compared to 99.5% for a standard SSD and 95% for a standard HDD. Because of this, it is advised to utilize premium SSD disks on production or critical virtual machines in Azure.

Now that you understand the various factors that impact disk performance, we will now learn about disk caching and its effect on performance.