Azure Disk Storage Options Explained

By Ayesha Ali | Microsoft Azure

Jul 26

When migrating your data center from on premises to Azure, you have a lot of disk storage options available. It is very common to get confused in a lot of options. In this article we'll be covering most of the common storage options available in Azure.

Difference Between Managed Disks and Unmanaged Disks

Microsoft has launched a new type of Disk i.e. Managed Disk. This article discusses the differences between Azure Managed and Unmanaged disks

In unmanaged disks, you have to create storage accounts to hold the disks (VHD files) for your Azure VMs.

With Managed Disks, you are no longer limited by the storage account limits. You can have one storage account per Azure region.

Benefits of Using Managed Azure Disk Storage:

  1. Managed Disks provides better reliability for Availability Sets by ensuring that the disks of VMs in an Availability Set are sufficiently isolated from each other to avoid single points of failure
  2. Azure Disks are designed for 99.999% availability.
  3. Granular access control: You can grant access to only the operations a person needs to perform their job. For example, if you don't want a person to copy a managed disk to a storage account, you can choose not to grant access to the export action for that managed disk.


Managed Disks

Unmanaged Disks


Is an ARM (Azure Resource Manager) object (resource)

Is not an ARM resource, but a file (.vhd) residing on an Azure Storage Account. The latter is an ARM object


The managed disks sizes are fixed (and can be resized). Which means that you cannot choose a custom size. You will need to pick up from a list.

You can choose the disk size during the provisioning (and can be resized) when using Standard Storage.


A managed disk has a predictable performance, with Standard storage (500 IOPS) or Premium storage (Depends on the disk).

Only premium storage disks have a predictable performance (depends on the disk). Standard storage has a predictable performance (500 IOPS) unless they are impacted by the Storage Account performance limits (A maximum of 40 disks per standard storage account is recommended, otherwise disks can be throttled).


When placing Azure Virtual Machines using managed disks under an Availability Set, disks are placed on different fault domains in order to achieve the better SLA (The Availability Set SLA is only for compute)

When placing Azure Virtual Machines using unmanaged disks under an Availability Set, there is no guarantee that the disks are placed on different fault domains, even if they are on different Storage Accounts.





ADE, SSE (Coming soon)


Managed and Unmanaged Disks Pricing

Pricing of disks depends upon various factor. Usually managed disks are 3 times expensive than unmanaged disks. 

Azure Disks Comparison

The following table provides a comparison of Standard HDD, Standard SSD, and Premium SSD for unmanaged and managed disks to help you decide what to use.

Azure Premium Disk

Standard SSD Disk (preview)

Azure Standard HDD Disk

Disk Type

Solid State Drives (SSD)

Solid State Drives (SSD)

Hard Disk Drives (HDD)


SSD-based high-performance, low-latency disk support for VMs running IO-intensive workloads or hosting mission critical production environment

More consistent performance and reliability than HDD. Optimized for low-IOPS workloads

HDD-based cost-effective disk for infrequent access


Production and performance sensitive workloads

Web servers, lightly used enterprise applications and Dev/Test

Backup, Non-critical, Infrequent access

Disk Size

P4: 32 GiB (Managed Disks only)
P6: 64 GiB (Managed Disks only)
P10: 128 GiB
P15: 256 GiB (Managed Disks only)
P20: 512 GiB
P30: 1024 GiB
P40: 2048 GiB
P50: 4095 GiB

Managed Disks only:
E10: 128 GiB
E15: 256 GiB
E20: 512 GiB
E30: 1024 GiB
E40: 2048 GiB
E50: 4095 GiB

Unmanaged Disks: 1 GiB – 4 TiB (4095 GiB)

Managed Disks:
S4: 32 GiB
S6: 64 GiB
S10: 128 GiB
S15: 256 GiB
S20: 512 GiB
S30: 1024 GiB
S40: 2048 GiB
S50: 4095 GiB

Max Throughput per Disk

250 MiB/s

Upto 60 MiB/s

Upto 60 MiB/s

Max IOPS per Disk

7500 IOPS

Upto 500 IOPS

Upto 500 IOPS

Reference Article:

Disk Caching in Azure

A disk cache is a cache memory that is used to speed up the process of storing and accessing data from the hard disk. In Azure we have Premium Disks for Caching. Microsoft recommends to enable caching for frequently used data

Azure Disk Caching Pricing

There is no additional price for caching

Storage Tiers in Azure

There are three types of Azure disk storage tiers, so that you can store your data in most cost-effective manner and depending on how you use it

Hot Access Tier

Hot Access Tier is the one where the frequently used data resides. It has high storage costs and low access costs. For critical frequently used applications like SQL, Microsoft always recommends using Standard/Premium SSD as SSD already has Caching in it.

Cool Access Tier

Cool Access Tier is the one where infrequently accessed data resides and stored for at least 30 day. It has lower storage costs and higher access costs compared to hot storage

Archive Access Tier

Archive Access Tier is used for storing data that is rarely accessed and stored for at least 180 days with flexible latency requirements. The archive storage tier is only available at the blob level and not at the storage account level.

Reference Article:

Conversion of HDD to SSD

We have discussed about Azure disk storage options in our last article. Today, we’ll talk about converting HDD to SSD.


To get the hassle-free migration of HDD to SSD drive done, you need to get the important prerequisites checked first. These prerequisites are mentioned below.

  1. You should first check whether the SSD is available in the destination region.
  2. Your Drive should be a Managed Disk.
  3. Your Size of VM should support Premium SSD if you wish to migrate to it.
  4. You should schedule the migration of your disks storage during a pre-existing maintenance window, as the conversion requires a restart of the VM.


Coming to the procedures conducted in PowerShell. You should be very careful when running the below mentioned commands to generate effectiveness, otherwise, you may end up making the whole procedure a liability.


You need to run Connect-AzureRmAccount in PowerShell with Azure RM module included in it to create a connection with Azure.

The following example shows how to switch a single disk of a VM from standard HDD to standard SSD, and vice versa.

# the name of the disk you want to convert

$diskName = 'yourDiskName'

# resource group that contains the managed disk

$rgName = 'yourResourceGroupName'

# Choose between Standard_LRS and StandardSSD_LRS based on your scenario

$storageType = 'StandardSSD_LRS'

$disk = Get-AzureRmDisk -DiskName $diskName -ResourceGroupName $rgName

# Get parent VM resource

$vmResource = Get-AzureRmResource -ResourceId $disk.ManagedBy

# Stop and deallocate the VM before changing the storage type

Stop-AzureRmVM -ResourceGroupName $vmResource.ResourceGroupName -Name $vmResource.Name -Force

$vm = Get-AzureRmVM $vmResource.ResourceGroupName -Name $vmResource.ResourceName

# Update the storage type

$diskUpdateConfig = New-AzureRmDiskUpdateConfig -AccountType $storageType -DiskSizeGB $disk.DiskSizeGB

Update-AzureRmDisk -DiskUpdate $diskUpdateConfig -ResourceGroupName $rgName ` -DiskName $disk.Name

# Starting the Vm after successful conversion

Start-AzureRmVM -ResourceGroupName $vm.ResourceGroupName -Name $vm.Name

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About the Author

Microsoft Technology Associate based in Ireland working with Communication Square.