Slow IOPS in Azure VM’s? not anymore!

— UPDATE 31-12-2019 — New disk sizes P1-P3 & E1-E3

In Azure there are several ways to implement your VM storage. I get a lot of complaints about slow storage in Azure. In this article I will try to explain why this might be slow, and what you can do about it. There are multiple locations where the limit might be hit. So I will address all in the following topics.

Virtual machine type

The first limitation might be coming from your virtual machine. Each type has its own total IOPS limit. Thus by adding more disk or faster disk than the type and size allows will not make any speed difference in the end. One of the obvious reasons for faster disk performance is to use SSD disks instead of HDD.

Example of an IOPS limit on VM type

But keep in mind, not all virtual machines do support Premium SSD Storage, with an effective limit of 500 IOPS per disk, like in the Av2 series. And then there is host caching, that effects performance as well. A few examples:

Av2 VM: Standard_A2_v2

Max data disksCached
44 x 500

B VM: Standard_B2s

Max data disksCached

DSv3-Series: Standard_D4s_v3

Max data disksCached

If you need extreme disk performance you can choose to go ahead with Lsv2-series Storage optimized vm’s. These can deliver up to 3.8 milion IOPS using NVMe disks. (max 10×1.92TB)

So choosing the right VM is very important. The following Virtual Machine Series do NOT support Premium SSD storage:
– Av2-Series
– Dv2-Series
– Dv3-Series
– Ev3-Series
– G-Series
– NC-Series
– NV-Series

Storage accounts

If you have any virtual machines with unmanaged disks, it is important to keep in mind that each storage account has an IOPS limit of 20.000. This means that 5 premium terabyte SSD disks will exceed this maximum. Therefore it is recommended to use managed disk, besides all other benefits. (one downside of managed disks is that you pay for the full disk on HDD)

HDD & SSD Standard disks

By default HDD disks have a low limit on IOPS. Depending on the size this can increase up to 6000 IOPS.

Standard SSD SizeDisk size in GiBIOPS per diskThroughput per disk
E14Up to 120 Up to 25 MiB/sec
E28Up to 120 Up to 50 MiB/sec
E316Up to 120 Up to 60 MiB/sec
E432Up to 120 Up to 60 MiB/sec
E664Up to 240 Up to 60 MiB/sec
E10128Up to 500 Up to 60 MiB/sec
E15256Up to 500 Up to 60 MiB/sec
E20512Up to 500 Up to 60 MiB/sec
E301024Up to 500 Up to 60 MiB/sec
E402048Up to 500 Up to 60 MiB/sec
E504096Up to 500 Up to 60 MiB/sec
E608192Up to 2000 Up to 400 MiB/sec
E7016384Up to 4000 Up to 600 MiB/sec
E8032767Up to 6000 Up to 750 MiB/sec

SSD Premium disks

Premium disks do support higher IOPS and throughput. In the following table you can review the performance of each disk. A new feature (in preview now!) is burstable disks. This means that disks can burst for 30 minutes in a row when needed. Bursting is credit based, which means that if you require only half of your IOPS during normal load, you can burst the unused IOPS during peak times.

SSD Size
Disk size
in GiB
IOPS per diskMax Burst IOPSThroughput per disk
P14Up to 1203500 / 30 minUp to 25 MiB/sec
P28Up to 120 3500 / 30 min Up to 50 MiB/sec
P316Up to 120 3500 / 30 min Up to 60 MiB/sec
P432Up to 120 3500 / 30 min Up to 60 MiB/sec
P664Up to 2403500 / 30 min Up to 60 MiB/sec
P10128Up to 5003500 / 30 min Up to 60 MiB/sec
P15256Up to 5003500 / 30 min Up to 60 MiB/sec
P20512Up to 5003500 / 30 min Up to 60 MiB/sec
P301024Up to 5003500 / 30 min Up to 60 MiB/sec
P402048Up to 5003500 / 30 min Up to 60 MiB/sec
P504096Up to 5003500 / 30 min Up to 60 MiB/sec
P608192Up to 20003500 / 30 min Up to 400 MiB/sec
P7016384Up to 40003500 / 30 min Up to 600 MiB/sec
P8032767Up to 60003500 / 30 min Up to 750 MiB/sec

Ultra SSD

At the moment of writing Ultra SSDs are still in preview only and are limited available. Where you would pay per GB on traditional disks, Ultra SSD will charge you extra on reserved IOPS capacity. Ultra SSD is an layer over Premium SSD where you can reserve extra IOPS performance (and be charged for it).

Some key capabilities of Ultra SSD are:

  • Disk capacity: Ultra SSD capacity ranges from 4 GiB up to 64 TiB.
  • Disk IOPS: Ultra SSD support IOPS limits of 300 IOPS/GiB, up to a maximum of 160 K IOPS per disk. To achieve the IOPS that you provisioned, ensure that the selected Disk IOPS are less than the VM IOPS. The minimum disk IOPS are 100 IOPS.
  • Disk throughput: With ultra SSD, the throughput limit of a single disk is 256 KiB/s for each provisioned IOPS, up to a maximum of 2000 MBps per disk (where MBps = 10^6 Bytes per second). The minimum disk throughput is 1 MiB.
  • Ultra SSDs support adjusting the disk performance attributes (IOPS and throughput) at runtime without detaching the disk from the virtual machine. Once a disk performance resize operation has been issued on a disk, it can take up to an hour for the change to actually take effect.

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