Understanding Block Storage in Microsoft Azure

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When running workloads in the Public Cloud such as Microsoft Azure, you have a bunch of options when it comes to block storage. How do you know which one to pick? There are alot of choices–tradeoffs, features and sprawl can also occur. In this blog I will cover the different types of disks available to help educate you on some of the purposes and limitations of each.

Azure Storage Data Services

The Azure Storage platform includes the following data services:

  • Azure Blobs: A massively scalable object store for text and binary data. Also includes support for big data analytics through - Data Lake Storage Gen2.
  • Azure Files: Managed file shares for cloud or on-premises deployments.
  • Azure Queues: A messaging store for reliable messaging between application components.
  • Azure Tables: A NoSQL store for schemaless storage of structured data.
  • Azure Disks: Block-level storage volumes for Azure VMs.

For this sake of this article we will be diving in to the different types of Azure Disks (Also known as Managed Disks).

Types of Azure Disks

Today Azure has 4 types of Managed disks, designed to address different requirements.

Type of DiskDescription
Standard HDDsDesigned for Backup, Non-Critical and Infrequently Accessed Storage
Standard SSDsDesigned for Web Servers, Lightly used Apps and Dev/Test
Premium SSDsProduction and Performance Sensitive Workloads
Ultra SSDsIO-Intensive Workloads such as SAP HANA and other Top Tier Databases and transaction-heavy workloads

Each one of these disks has some limits to be aware of, whether it is Disk Capacity, Disk Sizes, Disk Throughput and Disk IOPs

Type of DiskMax CapacityMax ThroughputMax IOPs
Standard HDDs32,767 GiB500 MB/s2,000
Standard SSDs32,767 GiB750 MB/s6,000
Premium SSDs32,767 GiB900 MB/s20,000
Ultra SSDs65,536 gibibyte (GiB)4,000 MB/s160,000

One other consideration to think about is features, each disk types have the ability to be multi-attached, encrypted, backed up and replicated. However, only some of the features are available with each one.

Type of DiskMulti-Attach (Shared Disks)BackupReplicationSnapshot
Standard HDDsYes1YesYesYes
Standard SSDsYes1YesYesYes
Premium SSDsYes1YesYesYes
Ultra SSDsYes2NoNoNo

Based off these matrices we can see how each one of the disks can match up to their designed requirement. In the next section we will dive a little bit more into each limit–Considerations, Capacity, Throughput and IOPs.

Considerations

When choosing a disk to use in the Cloud there are many considerations to think about. Do you need specific features? Do you need Performance? Do you need Cost Efficency? Do you need Availability/Durability?

When we think about features, this can drive what disk you want to use, thinking about the section above depending on what features you need will decide what kind of Azure Disk you need to use.

When we think about Performance, What are your throughput requirements? What are your IOPs requirements? What are your latency requirements? If you require an extremely fast disk with low latency–Ultra SSD is your option. If you need a cheap disk to land some archive files then a Standard HDD may fit your needs. Along with performance we may think about how that translates to Cost Efficency.

When we think about the cost efficencies, this can be something that we want to keep an eye on. When speaking to customers, storage is normally the largest cost when running in the Public Cloud. Having to balance performance and capacity is important, as you pay for everything you provision vs what you actually use–it is even more important to rightsize your disk.

Lastly, when we think about availability and durability in Azure this is where they excel. Most disks in Azure are 99.999% of availability. If you are using Locally-redundant storage (LRS), it provides at least 99.999999999% (11 nines). If you are using Zone-redundant storage (ZRS), it offers durability for storage resources of at least 99.9999999999% (12 nines) over a given year.

Capacity Options

Standard HDD’s start at 32GiB in size and can go to 32,768 in size. a Standard HDD size aligns with binary Disk sizes so if you want a 40GiB disk you cannot, you need to choose a 64 GiB disk. What happens if you want a 4.1TiB disk? Well you need to go out and deploy a 8192 GiB disk and pay almost twice as much.

For Standard HDD these are the capacity options.

Standard Disk TypesS4S6S10S15S20S30S40S50S60S70S80
Disk size in GiB32641282565121,0242,0484,0968,19216,38432,767

For Standard SDD these are the capacity options.

Standard SSD TypesE1E2E3E4E6E10E15E20E30E40E50E60E70E80
Disk size in GiB481632641282565121,0242,0484,0968,19216,38432,767

For Premium SSD these are the capacity options.

Premium SSD TypesP1P2P3P4P6P10P15P20P30P40P50P60P70P80
Disk size in GiB481632641282565121,0242,0484,0968,19216,38432,767

For Ultra SSD these are the capacity options.

Disk Size (GiB)
4
8
16
32
64
128
256
512
1,024-65,5363 4

As you can see as the disk gets larger, the effencies of storage go down as well. There are also othe considerations to think about. What happens if you need to replace a disk? or Resize a disk? Most of these operations require the VM to be Stopped in order for this change to be made. If downtime is hard to come by in your environment you may also over-provision from the start to meet these requirements.

Throughput Options

A consideration of throughput with Standard HDD, Standard SDD and Premium SSD is that performance comes with capacity. If you already haven’t had to oversize your disk just to be able to meet the capacity availability, you may now increase it more to be able to meet your performance requirements.

For Standard HDD these are the throughput for each disk capacity.

Standard Disk TypesS4S6S10S15S20S30S40S50S60S70S80
Disk size in GiB32641282565121,0242,0484,0968,19216,38432,767
Throughput per diskUp to 60 MB/secUp to 60 MB/secUp to 60 MB/secUp to 60 MB/secUp to 60 MB/secUp to 60 MB/secUp to 60 MB/secUp to 60 MB/secUp to 300 MB/secUp to 500 MB/secUp to 500 MB/sec

For Standard SSD these are the throughput for each disk capacity. We also now have the option of Bursting. Bursting provides better tolerence for unpredictable IO patterns but could also have a cost associated with it.

Standard SSD TypeE2E3E4E6E10E15E20E30E40E50E60E70E80
Disk size in GiB481632641282565121,0242,0484,0968,19216,384
Throughput per diskUp to 60 MB/secUp to 60 MB/secUp to 60 MB/secUp to 60 MB/secUp to 60 MB/secUp to 60 MB/secUp to 60 MB/secUp to 60 MB/secUp to 60 MB/secUp to 60 MB/secUp to 60 MB/secUp to 400 MB/secUp to 600 MB/sec
Max burst throughput per disk150 MB/sec150 MB/sec150 MB/sec150 MB/sec150 MB/sec150 MB/sec150 MB/sec150 MB/sec250 MB/secN/AN/AN/AN/A

For Premium SSD these are the throughput for each disk capacity. We also now have the option of Bursting. Bursting provides better tolerence for unpredictable IO patterns but could also have a cost associated with it.

Premium SSD TypesP1P2P3P4P6P10P15P20P30P40P50P60P70P80
Disk size in GiB481632641282565121,0242,0484,0968,19216,38432,767
Provisioned Throughput per disk25 MB/sec25 MB/sec25 MB/sec25 MB/sec50 MB/sec100 MB/sec125 MB/sec150 MB/sec200 MB/sec250 MB/sec250 MB/sec500 MB/sec750 MB/sec900 MB/sec
Max burst throughput per disk170 MB/sec170 MB/sec170 MB/sec170 MB/sec70 MB/sec170 MB/sec170 MB/sec170 MB/sec1,000 MB/sec41,000 MB/sec41,000 MB/sec41,000 MB/sec41,000 MB/sec41,000 MB/sec4

For Ultra SSD you can provision throughput independent of capacity, however each capacity does have a Throughput Cap. Keep in mind the minimum Throughput must be able to the capacity of the disk and each MBps will have a cost associated with it.

Disk Size (GiB)Throughput Cap (MBps)
4300
8600
161,200
322,400
644,000
1284,000
2564,000
5124,000
1,024-65,536 3 44,000

Even through the maximum throughput is 4,000 MBps, it also requires an Azure Instance capabale of pushing that amount of throughput.

As we can see for each disk type each one has a minimum capacity to get the max throughput for that disk type. Be aware of this when creating your disk to make sure each has the performance capabilitiy required for your workload.

IOPS Options

As with throughput, each one of the disks also has a limit of how many IOPs a disk can perform based on the disk capacity size.

For Standard HDD these are the IOPs for each disk capacity.

Standard Disk TypesS4S6S10S15S20S30S40S50S60S70S80
Disk size in GiB32641282565121,0242,0484,0968,19216,38432,767
IOPS per diskUp to 500Up to 500Up to 500Up to 500Up to 500Up to 500Up to 500Up to 500Up to 1,300Up to 2,000Up to 2,000

For Standard SSD these are the throughput for each disk capacity. We still have the option of Bursting.

Standard SSD TypesE2E3E4E6E10E15E20E30E40E50E60E70E80
Disk size in GiB481632641282565121,0242,0484,0968,19216,384
IOPS per diskUp to 500Up to 500Up to 500Up to 500Up to 500Up to 500Up to 500Up to 500Up to 500Up to 500Up to 500Up to 2,000Up to 4,000
Max burst IOPS per disk6006006006006006006006001000N/AN/AN/AN/A

For Premium SSDthese are the throughput for each disk capacity. We still have the option of Bursting.

Premium SSD TypesP1P2P3P4P6P10P15P20P30P40P50P60P70P80
Disk size in GiB481632641282565121,0242,0484,0968,19216,38432,767
Provisioned IOPS per disk1201201201202405001,1002,3005,0007,5007,50016,00018,00020,000
Max burst IOPS per disk3,5003,5003,5003,5003,5003,5003,5003,50030,000530,000530,000530,000530,000530,0005

For Ultra SSD you can provision IOPs independent of capacity, however each capacity does have a IOP Cap. While you can provision IOPs independent of capacity keep in mind there is a per IOP cost that can climb pretty quickly.

Disk Size (GiB)IOPS Cap
41,200
82,400
164,800
329,600
6419,200
12838,400
25676,800
512153,600
1,024-65,5363 4160,000

Even through the maximum IOPs is 160,000 it also requires an Azure Instance capabale of pushing that amount of IOPS.

Conclusion

Public Cloud Storage does provide you many options and flexibility, but with that comes many options, tradeoffs and sprawl. Do you need Performance? What happens if you want it to be cost effecient? Some of these decisions can sometimes be hard to make and ultimately you need to limit yourself in this area. There are products out there that can help with this–however, I will keep that topic for a future post.

Hopefully this post helped you understand the current types of block storage available in Microsoft Azure today and has educated you a bit on each capability as well. Next post will include the many o ptions available within Amazon Web Services.



  1. Can only be used for data disks, not OS disks. Host Caching and Disk bursting is not available. Only basic disks can be used with some versions of WSFC. Azure Site Recovery is not available. Azure Disk Encryption is not supported. ↩︎

  2. Only basic disks can be used with some versions of WSFC. Azure Disk Encryption is not supported. ↩︎

  3. Azure ultra disks offer up to 32 TiB per region per subscription by default, but ultra disks support higher capacity by request. To request an increase in capacity, request a quota increase or contact Azure Support. ↩︎

  4. Sizes increase by incement of 1 TiB ↩︎

  5. Applies only to disks with on-demand bursting enabled. ↩︎

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