Understanding Azure disk bursting

Currently, there are two managed disk types that can burst, premium SSDs, and standard SSDs. Other disk types cannot currently burst. There are two models of bursting for disks:

An on-demand bursting model, where the disk bursts whenever its needs exceed its current capacity. This model incurs additional charges anytime the disk bursts. On-demand bursting is only available for premium SSDs larger than 512 GiB.

A credit-based model, where the disk will burst only if it has burst credits accumulated in its credit bucket. This model does not incur additional charges when the disk bursts. Credit-based bursting is only available for premium SSDs 512 GiB and smaller, and standard SSDs 1024 GiB and smaller.

Azure premium SSDs can use either bursting model, but standard SSDs currently only offer credit-based bursting.

On-demand bursting

Premium SSDs using the on-demand bursting model of disk bursting can burst beyond original provisioned targets, as often as needed by their workload, up to the max burst target. For example, on a 1-TiB P30 disk, the provisioned IOPS is 5000 IOPS. When disk bursting is enabled on this disk, your workloads can issue IOs to this disk up to the max burst performance of 30,000 IOPS and 1,000 MBps. For the max burst targets on each supported disk, see Scalability and performance targets for VM disks.

If you expect your workloads to frequently run beyond the provisioned perf target, disk bursting won’t be cost-effective. In this case, we recommend that you change your disk’s performance tier to a higher tier instead, for better baseline performance. Review your billing details and assess that against the traffic pattern of your workloads.

Before you enable on-demand bursting, understand the following:

  • On-demand bursting cannot be enabled on a premium SSD that has less than or equal to 512 GiB. Premium SSDs less than or equal to 512 GiB will always use credit-based bursting.
  • On-demand bursting is only supported on premium SSDs. If a premium SSD with on-demand bursting enabled is switched to another disk type, then disk bursting is disabled.
  • On-demand bursting doesn’t automatically disable itself when the performance tier is changed. If you want to change your performance tier but do not want to keep disk bursting, you must disable it.
  • On-demand bursting can only be enabled when the disk is detached from a VM or when the VM is stopped. On-demand bursting can be disabled 12 hours after it has been enabled.