Slow IOPS in Azure VM’s? not anymore!

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
IOPS
Cached
MBps
Uncached
IOPS
Uncached
MBps
44 x 500

B VM: Standard_B2s

Max data disksCached
IOPS
Cached
MBps
Uncached
IOPS
Uncached
MBps
4160015128015

DSv3-Series: Standard_D4s_v3

Max data disksCached
IOPS
Cached
MBps
Uncached
IOPS
Uncached
MBps
88000100640096

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 limit of 300 IOPS for basic disks, and 500 IOPS for standard disks. SSD Standard disks utilize a low latency disk but is restricted to 500 IOPS as well. The largest sizes have been left out to keep an good overview, but the biggest disk is 16TiB

Standard
SSD size
E4E6E10E15E20E30E40E50
Disk size in GiB3264128256512102420484095
IOPS per
disk
Up to
120
Up to
240
Up to
500
Up to
500
Up to
500
Up to
500
Up to
500
Up to
500
Throughput per diskUp to
25 MiB/sec
Up to
50 MiB/sec
Up to
60 MiB/sec
Up to
60 MiB/sec
Up to
60 MiB/sec
Up to
60 MiB/sec
Up to
60 MiB/sec
Up to
60 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. The largest sizes have been left out to keep an good overview, but the biggest disk is 16TiB

D sizes P4P6P10P15P20P30P40P50
Disk size
in GiB
3264128256512102420484096
IOPS per
disk
Up to
120
Up to
240
Up to
500
Up to
1100
Up to
2300
Up to
5000
Up to
7500
Up to
7500
Throughput per diskUp to
25 MiB/sec
Up to
50 MiB/sec
Up to
100 MiB/sec
Up to
125 MiB/sec
Up to
150 MiB/sec
Up to
200 MiB/sec
Up to
250 MiB/sec
Up to
250 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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