Azure Premium SSD now supports burst mode

Microsoft have made a number of changes to their Premium SSD managed disk service, 3 new small sizes (4, 8, & 16 GiB) and have also introduced burst mode for disk sizes P20 and below (<= 512GiB). Disk bursting allows your disks to increase both IOPS and Throughput for up to 30 minutes, this capability is based upon a credit system.

The credit system works by evaluating the actual traffic against the provisioned performance targed of the disk; any under utilization is added to a credit bucket. If you require performance above the provisioned target then any over performance consumed credits from the bucket. For example A P1 disk has a provisioned target of 120 IOPS and 25 MBps. If the actual traffic on the disk was 100 IOPS and 20 MBps in the past 1 second interval, then the unused 20 IOs and 5 MB are credited to the burst bucket of the disk. Credits in the burst bucket can later be used when the traffic exceeds the provisioned target, up to the max burst limit. The max burst limit defines the ceiling of disk traffic even if you have burst credits to consume from. In this case, even if you have 10,000 IOs in the credit bucket, a P1 disk cannot issue more than the max burst of 3,500 IO per sec.

 

Disk size

Provisioned IOPS

Provisioned bandwidth

Max burst IOPS

Max burst bandwidth

P1

4 GiB

120

25 MiB/second

3,500

170 MiB/second

P2

8 GiB

120

25 MiB/second

3,500

170 MiB/second

P3

16 GiB

120

25 MiB/second

3,500

170 MiB/second

P4

32 GiB

120

25 MiB/second

3,500

170 MiB/second

P6

64 GiB

240

50 MiB/second

3,500

170 MiB/second

P10

128 GiB

500

100 MiB/second

3,500

170 MiB/second

P15

256 GiB

1,100

125 MiB/second

3,500

170/MiB/second

P20

512 GiB

2,300

150 MiB/second

3,500

170 MiB/second

The good news is disk bursting is enabled by default on all new deployments of the disk sizes that support it. Existing disk sizes, if they support disk bursting, can enable bursting through either of the following methods:

  • Detach and reattach the disk.
  • Stop and start the VM.

Bellow is an example of how to detach and reattach a disk using PowerShell:

$rgName = “myResourceGroup”
$vmName = “myVM”
$location = “East US”
$dataDiskName = “myDisk”
$VM = Get-AzVM -ResourceGroupName $rgName -Name $vmName
Remove-AzVMDataDisk -VM $VirtualMachine -Name $dataDiskName
Update-AzVM -ResourceGroupName $rgName -VM $VM
$disk = Get-AzDisk -ResourceGroupName $rgName -DiskName $dataDiskName
$vm = Add-AzVMDataDisk -CreateOption Attach -Lun 0 -VM $vm -ManagedDiskId $disk.Id
Update-AzVM -VM $vm -ResourceGroupName $rgName

Below is an example of how to detach and reattach a disk using PowerShell:

$rgName = “myResourceGroup”
$vmName = “myVM”
Stop-AzVM -ResourceGroupName $rgName -Name $vmName
Start-AzVM -ResourceGroupName $rgName ” -Name $vmName

  

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