Optimize performance and costs using performance-scaling options

• 5 minutes

By migrating your organization's critical workload to Azure, you can provide a range of infrastructure requirements, like scalable performance, built-in security, durability, and cost optimization.

Many of these infrastructure requirements are directly associated with block storage, which is the foundation of Azure Disk Storage.

The type and size of the disk you select for your critical applications directly affects the applications' performance and can generate higher costs if you don't select the appropriate option.

To help you optimize performance and costs, Azure Disk Storage also offers capabilities for scaling your performance to meet the needs of your workloads, and keep costs under control.

The following sections discussing performance options don't apply to Ultra disks or Premium SSD v2 managed disks. The performance attributes of Ultra disks and Premium SSD v2 managed disks can be independently adjusted as needed, and these disks don't have tiers or bursting.

Performance tiers for Azure Disk Storage

For Premium SSD managed disks only, you can adjust and balance the IOPS and throughput of your disks by selecting the right performance tier for your needs. To select the right combination, you should be aware of your application requirements. Applications that have high I/O, like database servers or online transactional processing systems, require higher IOPS.

You might have planned events, like a seasonal promotion or performance testing, during which the application requires higher demands on performance on a temporary basis. To optimize costs, you can change the performance tier on Premium SSD disks without increasing the size of the disks when you need to meet a higher performance demand. For example, your marketing applications are provisioned to use a Premium SSD disk with a P4 performance tier limited to 120 IOPS and 25 MB/s. Because of a seasonal sale, the interest for your marketing application increases dramatically, and you want to meet the higher capacity demands on a temporary basis. You can increase the performance tier of your P4 disk to a higher tier, such as P30 with 5,000 IOPS and 200 MB/s of throughput. When your marketing campaign is over, you can change the disk tier back to the original P4 tier. During the period when you use a higher performance tier, you're charged for the price of that tier. In this example, you're charged the price of a P30.

Change the performance tier on Premium SSD disks while they are in use

You can change the performance tier of a Premium SSD disk without downtime and without dismounting the disk from the virtual machine (VM).

You can change the performance tier of the disk by using the Azure CLI or the Azure portal.

In the Azure CLI, use the following commands to change the disk performance tier:

subscriptionId="yourSubscriptionID"
resourceGroupName="yourResourceGroupName"
diskName="yourDiskName"
performanceTier="yourDesiredPerformanceTier"


az login
az account set --subscription $subscriptionId

az disk update -n $diskName -g $resourceGroupName --set tier=$performanceTier

Azure disk bursting

For unplanned events requiring high performance for a short period of time, you can benefit from the disk bursting capabilities of Azure disks. Disk bursting can improve boot times, manage processing of small-batch jobs, and deal with unexpected traffic spikes.

Azure provides this functionality both for VMs and for disks, and you can use it independently.

VM bursting

VM bursting supports only the credit-based model for bursting, which doesn't require any configuration. While a VM is used, it accumulates credits when the resource's IOPS or throughput are less than the resource's performance target. You can use these credits to burst performance for up to 30 minutes at the maximum burst rate.

Disk bursting

Disk Storage has two models of bursting:

• Credit-based bursting model. A credit-based model, where the disk will burst only if it has burst credits accumulated in its credit bucket. This model doesn't incur extra charges when the disk bursts. Credit-based bursting is only available for Premium SSD managed disks 512 GiB and smaller, and standard SSDs 1,024 GiB and smaller.
• On-demand bursting model. An on-demand bursting model, where the disk bursts whenever its needs exceed its current capacity. This model incurs more charges anytime the disk bursts. On-demand bursting is only available for Premium SSD managed disks larger than 512 GiB. To configure on-demand bursting, you must detach the disk from the VM.

You can enable on-demand bursting by using Azure PowerShell, the Azure CLI, or an ARM template. You can enable this functionality on new and existing disks.

In Azure PowerShell, use the following command to create an empty data disk with on-demand bursting:

Set-AzContext -SubscriptionName "yourSubscriptionName"
$diskConfig = New-AzDiskConfig -Location "WestCentralUS" -CreateOption Empty -DiskSizeGB 1024 -SkuName Premium_LRS -BurstingEnabled $true
$dataDisk = New-AzDisk -ResourceGroupName "myResourceGroupDisk" -DiskName "myDataDisk" -Disk $diskConfig

Performance plus (preview)

The Input/Output Operations Per Second (IOPS) and throughput limits for Premium SSD, Standard SSD, and Standard HDD that are 513 GiB and larger can be increased by enabling performance plus. Enabling performance plus (preview) improves the experience for workloads that require high IOPS and throughput, such as database and transactional workloads. There's no extra charge for enabling performance plus on a disk.

For more information on performance plus, including the limitations, see Increase IOPS and throughput limits for Azure Premium SSDs and Standard SSD/HDDs

Costs

Before deciding on which disk type suits your needs the most, consider how the billing for that disk is done. The total cost of your disk is calculated differently for each disk type.

The following factors determine the cost of a disk:

• The region the disk is deployed in (all disks)
• The size of the disk (all disks)
• The number of transactions made involving the disk (all transactions for Standard HDD and Standard SSD. For Premium SSD, burst transactions only)
• The redundancy option selected (Standard SSD and Premium SSD only)
• The enabled/disabled setting for on-demand bursting (Premium SSD only)
• The disk's IOPS (Ultra Disks and Premium SSD v2 only)
• The disk's throughput (Ultra Disks and Premium SSD v2 only)

For more detail on the costs involved with managed disks, see the pricing page.

Transactions

On Azure, input/output operation per second (IOPS) and transactions are similar with one major exception:

A transaction on Azure is an I/O operation less than or equal to 256 KiBs of throughput. If your IO operation is larger than 256 KiBs of throughput, it requires multiple transactions. The number of transactions is calculated by dividing the I/O size by 256 KiBs.

For example, an IO with the size of 1024 KiBs (1 MiB) would be processed as four transactions on a Standard SSD disk.

Standard SSDs have a cap on the number of transactions that are billed in an hour. Once that cap is passed, the rest of your transactions during that hour are free. For details, see Standard SSD transaction caps.

Optimize performance and costs with the optimal option

Now that you understand how different performance indicators define the overall performance of an Azure disk, let's examine some use-case scenarios:

• Planned versus unplanned performance scaling: If you have a planned event like a marketing campaign that requires a sustained increase in disk performance, use performance tiers to better accommodate the increased load. However, if you can't plan ahead or can't accurately predict the performance pattern of your workloads, disk bursting would be a better choice. It provides you with a higher allowance beyond your provisioned target.
• Duration: For scenarios in which high demand results from short-running jobs or jitters in I/O scheduling, on-demand disk bursting is more cost-efficient because you pay only for the burst transactions. If your workload doesn't exceed the provisioned target, you pay only for the burst-enablement fee, which is a small fraction of the disk cost. In contrast, if you expect your workload to burst for days or even longer, performance tiers is the better option.

	Credit-based bursting	On-demand bursting	Changing performance tier
Scenario	Ideal for short-term scaling (30 minutes or less).	Ideal for short-term scaling (not time restricted).	Ideal if your workload would otherwise continually be running in burst.
Cost	Free.	Cost is variable. See Billing for details.	The cost of each performance tier is fixed. See Managed Disks pricing for details.
Availability	Only available for Premium SSD disks and Standard SSD disks 512 GiB and smaller.	Only available for Premium SSD disks larger than 512 GiB.	Available for all Premium SSD disk sizes.
Enablement	Enabled by default on eligible disks.	User must enable it.	User must manually change the tier.