Slow IOPS in Azure VM’s? not anymore!

Posted On June 11, 2019

— 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.

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 disks	Cached IOPS	Cached MBps	Uncached IOPS	Uncached MBps
4			4 x 500

B VM: Standard_B2s

Max data disks	Cached IOPS	Cached MBps	Uncached IOPS	Uncached MBps
4	1600	15	1280	15

DSv3-Series: Standard_D4s_v3

Max data disks	Cached IOPS	Cached MBps	Uncached IOPS	Uncached MBps
8	8000	100	6400	96

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 Size	Disk size in GiB	IOPS per disk	Throughput per disk
E1	4	Up to 120	Up to 25 MiB/sec
E2	8	Up to 120	Up to 50 MiB/sec
E3	16	Up to 120	Up to 60 MiB/sec
E4	32	Up to 120	Up to 60 MiB/sec
E6	64	Up to 240	Up to 60 MiB/sec
E10	128	Up to 500	Up to 60 MiB/sec
E15	256	Up to 500	Up to 60 MiB/sec
E20	512	Up to 500	Up to 60 MiB/sec
E30	1024	Up to 500	Up to 60 MiB/sec
E40	2048	Up to 500	Up to 60 MiB/sec
E50	4096	Up to 500	Up to 60 MiB/sec
E60	8192	Up to 2000	Up to 400 MiB/sec
E70	16384	Up to 4000	Up to 600 MiB/sec
E80	32767	Up 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.

Premium SSD Size	Disk size in GiB	IOPS per disk	Max Burst IOPS	Throughput per disk
P1	4	Up to 120	3500 / 30 min	Up to 25 MiB/sec
P2	8	Up to 120	3500 / 30 min	Up to 50 MiB/sec
P3	16	Up to 120	3500 / 30 min	Up to 60 MiB/sec
P4	32	Up to 120	3500 / 30 min	Up to 60 MiB/sec
P6	64	Up to 240	3500 / 30 min	Up to 60 MiB/sec
P10	128	Up to 500	3500 / 30 min	Up to 60 MiB/sec
P15	256	Up to 500	3500 / 30 min	Up to 60 MiB/sec
P20	512	Up to 500	3500 / 30 min	Up to 60 MiB/sec
P30	1024	Up to 500	3500 / 30 min	Up to 60 MiB/sec
P40	2048	Up to 500	3500 / 30 min	Up to 60 MiB/sec
P50	4096	Up to 500	3500 / 30 min	Up to 60 MiB/sec
P60	8192	Up to 2000	3500 / 30 min	Up to 400 MiB/sec
P70	16384	Up to 4000	3500 / 30 min	Up to 600 MiB/sec
P80	32767	Up to 6000	3500 / 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.