Frequently asked questions about Azure IaaS VM disks and managed and unmanaged premium disks

This article answers some frequently asked questions about Azure Managed Disks and Azure Premium SSD disks.

Managed Disks

What is Azure Managed Disks?

Managed Disks is a feature that simplifies disk management for Azure IaaS VMs by handling storage account management for you. For more information, see the Managed Disks overview.

If I create a standard managed disk from an existing VHD that's 80 GB, how much will that cost me?

A standard managed disk created from an 80-GB VHD is treated as the next available standard disk size, which is an S10 disk. You're charged according to the S10 disk pricing. For more information, see the pricing page.

Are there any transaction costs for standard managed disks?

Yes. You're charged for each transaction. For more information, see the pricing page.

For a standard managed disk, will I be charged for the actual size of the data on the disk or for the provisioned capacity of the disk?

You're charged based on the provisioned capacity of the disk. For more information, see the pricing page.

How is pricing of premium managed disks different from unmanaged disks?

The pricing of premium managed disks is the same as unmanaged premium disks.

Can I change the storage account type (Standard or Premium) of my managed disks?

Yes. You can change the storage account type of your managed disks by using the Azure portal, PowerShell, or the Azure CLI.

Can I use a VHD file in an Azure storage account to create a managed disk with a different subscription?

Yes.

Can I use a VHD file in an Azure storage account to create a managed disk in a different region?

No.

Are there any scale limitations for customers that use managed disks?

Managed Disks eliminates the limits associated with storage accounts. However, the maximum limit is 50,000 managed disks per region and per disk type for a subscription.

Can I take an incremental snapshot of a managed disk?

No. The current snapshot capability makes a full copy of a managed disk.

Can VMs in an availability set consist of a combination of managed and unmanaged disks?

No. The VMs in an availability set must use either all managed disks or all unmanaged disks. When you create an availability set, you can choose which type of disks you want to use.

Is Managed Disks the default option in the Azure portal?

Yes.

Can I create an empty managed disk?

Yes. You can create an empty disk. A managed disk can be created independently of a VM, for example, without attaching it to a VM.

What is the supported fault domain count for an availability set that uses Managed Disks?

Depending on the region where the availability set that uses Managed Disks is located, the supported fault domain count is 2 or 3.

How is the standard storage account for diagnostics set up?

You set up a private storage account for VM diagnostics.

What kind of Role-Based Access Control support is available for Managed Disks?

Managed Disks supports three key default roles:

  • Owner: Can manage everything, including access
  • Contributor: Can manage everything except access
  • Reader: Can view everything, but can't make changes

Is there a way that I can copy or export a managed disk to a private storage account?

You can generate a read-only shared access signature (SAS) URI for the managed disk and use it to copy the contents to a private storage account or on-premises storage. You can use the SAS URI using the Azure portal, Azure PowerShell, the Azure CLI, or AzCopy

Can I create a copy of my managed disk?

Customers can take a snapshot of their managed disks and then use the snapshot to create another managed disk.

Are unmanaged disks still supported?

Yes, both unmanaged and managed disks are supported. We recommend that you use managed disks for new workloads and migrate your current workloads to managed disks.

If I create a 128-GB disk and then increase the size to 130 GiB, will I be charged for the next disk size (256 GiB)?

Yes.

Can I create locally redundant storage, geo-redundant storage, and zone-redundant storage managed disks?

Azure Managed Disks currently supports only locally redundant storage managed disks.

Can I shrink or downsize my managed disks?

No. This feature is not supported currently.

Can I break a lease on my disk?

No. This is not supported currently as a lease is present to prevent accidental deletion when the disk is being used.

Can I change the computer name property when a specialized (not created by using the System Preparation tool or generalized) operating system disk is used to provision a VM?

No. You can't update the computer name property. The new VM inherits it from the parent VM, which was used to create the operating system disk.

Where can I find sample Azure Resource Manager templates to create VMs with managed disks?

Can I co-locate unmanaged and managed disks on the same VM?

No.

When creating a disk from a blob, is there any continually existing relationship with that source blob?

No, when the new disk is created it is a full standalone copy of that blob at that time and there is no connection between the two. If you like, once you've created the disk, the source blob may be deleted without affecting the newly created disk in any way.

Can I rename a managed or unmanaged disk after it has been created?

For managed disks you cannot rename them. However, you may rename an unmanaged disk as long as it is not currently attached to a VHD or VM.

Standard SSD disks

What are Azure Standard SSD disks? Standard SSD disks are standard disks backed by solid-state media, optimized as cost effective storage for workloads that need consistent performance at lower IOPS levels.

What are the regions currently supported for Standard SSD disks? All Azure regions now support Standard SSD disks.

Is Azure Backup available when using Standard SSDs? Yes, Azure Backup is now available.

How do I create Standard SSD disks? You can create Standard SSD disks using Azure Resource Manager templates, SDK, PowerShell or CLI. Below are the parameters needed in the Resource Manager template to create Standard SSD Disks:

  • apiVersion for Microsoft.Compute must be set as 2018-04-01 (or later)
  • Specify managedDisk.storageAccountType as StandardSSD_LRS

The following example shows the properties.storageProfile.osDisk section for a VM that uses Standard SSD Disks:

"osDisk": {
    "osType": "Windows",
    "name": "myOsDisk",
    "caching": "ReadWrite",
    "createOption": "FromImage",
    "managedDisk": {
        "storageAccountType": "StandardSSD_LRS"
    }
}

For a complete template example of how to create a Standard SSD disk with a template, see Create a VM from a Windows Image with Standard SSD Data Disks.

Can I convert my existing disks to Standard SSD? Yes, you can. Refer to Convert Azure managed disks storage from standard to premium, and vice versa for the general guidelines for converting Managed Disks. And, use the following value to update the disk type to Standard SSD. -AccountType StandardSSD_LRS

What is the benefit of using Standard SSD disks instead of HDD? Standard SSD disks deliver better latency, consistency, availability and reliability compared to HDD disks. Application workloads run a lot more smoothly on Standard SSD because of that. Note, Premium SSD disks are the recommended solution for most IO-intensive production workloads.

Can I use Standard SSDs as Unmanaged Disks? No, Standard SSDs disks are only available as Managed Disks.

Do Standard SSD Disks support "single instance VM SLA"? No, Standard SSDs do not have single instance VM SLA. Use Premium SSD disks for single instance VM SLA.

Migrate to Managed Disks

What changes are required in a pre-existing Azure Backup service configuration prior/after migration to Managed Disks?

No changes are required.

Will my VM backups created via Azure Backup service before the migration continue to work?

Yes, backups work seamlessly.

What changes are required in a pre-existing Azure Disks Encryption configuration prior/after migration to Managed Disks?

No changes are required.

Is automated migration of an existing virtual machine scale sets from unmanaged disks to Managed Disks supported?

No. You can create a new scale set with Managed Disks using the image from your old scale set with unmanaged disks.

Can I create a Managed Disk from a page blob snapshot taken before migrating to Managed Disks?

No. You can export a page blob snapshot as a page blob and then create a Managed Disk from the exported page blob.

Can I fail over my on-premises machines protected by Azure Site Recovery to a VM with Managed Disks?

Yes, you can choose to failover to a VM with Managed Disks.

Is there any impact of migration on Azure VMs protected by Azure Site Recovery via Azure to Azure replication?

Yes. Currently, Azure Site Recovery Azure to Azure protection for VMs with Managed Disks is only available as a public preview service.

Can I migrate VMs with unmanaged disks that are located on storage accounts that are or were previously encrypted to managed disks?

Yes

Managed Disks and Storage Service Encryption

Is Azure Storage Service Encryption enabled by default when I create a managed disk?

Yes.

Who manages the encryption keys?

Microsoft manages the encryption keys.

Can I disable Storage Service Encryption for my managed disks?

No.

Is Storage Service Encryption only available in specific regions?

No. It's available in all the regions where Managed Disks are available. Managed Disks is available in all public regions and Germany. It is also available in China, however, only for Microsoft managed keys, not customer managed keys.

How can I find out if my managed disk is encrypted?

You can find out the time when a managed disk was created from the Azure portal, the Azure CLI, and PowerShell. If the time is after June 9, 2017, then your disk is encrypted.

How can I encrypt my existing disks that were created before June 10, 2017?

As of June 10, 2017, new data written to existing managed disks is automatically encrypted. We are also planning to encrypt existing data, and the encryption will happen asynchronously in the background. If you must encrypt existing data now, create a copy of your disk. New disks will be encrypted.

Are managed snapshots and images encrypted?

Yes. All managed snapshots and images created after June 9, 2017, are automatically encrypted.

Can I convert VMs with unmanaged disks that are located on storage accounts that are or were previously encrypted to managed disks?

Yes

Will an exported VHD from a managed disk or a snapshot also be encrypted?

No. But if you export a VHD to an encrypted storage account from an encrypted managed disk or snapshot, then it's encrypted.

Premium disks: Managed and unmanaged

If a VM uses a size series that supports Premium SSD disks, such as a DSv2, can I attach both premium and standard data disks?

Yes.

Can I attach both premium and standard data disks to a size series that doesn't support Premium SSD disks, such as D, Dv2, G, or F series?

No. You can attach only standard data disks to VMs that don't use a size series that supports Premium SSD disks.

If I create a premium data disk from an existing VHD that was 80 GB, how much will that cost?

A premium data disk created from an 80-GB VHD is treated as the next-available premium disk size, which is a P10 disk. You're charged according to the P10 disk pricing.

Are there transaction costs to use Premium SSD disks?

There is a fixed cost for each disk size, which comes provisioned with specific limits on IOPS and throughput. The other costs are outbound bandwidth and snapshot capacity, if applicable. For more information, see the pricing page.

What are the limits for IOPS and throughput that I can get from the disk cache?

The combined limits for cache and local SSD for a DS series are 4,000 IOPS per core and 33 MiB per second per core. The GS series offers 5,000 IOPS per core and 50 MiB per second per core.

Is the local SSD supported for a Managed Disks VM?

The local SSD is temporary storage that is included with a Managed Disks VM. There is no extra cost for this temporary storage. We recommend that you do not use this local SSD to store your application data because it isn't persisted in Azure Blob storage.

Are there any repercussions for the use of TRIM on premium disks?

There is no downside to the use of TRIM on Azure disks on either premium or standard disks.

New disk sizes: Managed and unmanaged

What is the largest Managed disk size supported for operating system and data disks?

The partition type that Azure supports for an operating system disk is the master boot record (MBR). The MBR format supports a disk size up to 2 TiB. The largest size that Azure supports for an operating system disk is 2 TiB. Azure supports up to 32 TiB for managed data disks. Managed Disk sizes larger than 4 TiB are in preview. For more information on them see our blog post.

What is the largest Unmanaged Disk size supported for operating system and data disks?

The partition type that Azure supports for an operating system disk is the master boot record (MBR). The MBR format supports a disk size up to 2 TiB. The largest size that Azure supports for an operating system Unmanaged disk is 2 TiB. Azure supports up to 4 TiB for data Unmanaged disks.

What is the largest page blob size that's supported?

The largest page blob size that Azure supports is 8 TiB (8,191 GiB). The maximum page blog size when attached to a VM as data or operating system disks is 4 TiB (4,095 GiB).

Do I need to use a new version of Azure tools to create, attach, resize, and upload disks larger than 1 TiB?

You don't need to upgrade your existing Azure tools to create, attach, or resize disks larger than 1 TiB. To upload your VHD file from on-premises directly to Azure as a page blob or unmanaged disk, you need to use the latest tool sets listed below. We only support VHD uploads of up to 8 TiB.

Azure tools Supported versions
Azure PowerShell Version number 4.1.0: June 2017 release or later
Azure CLI v1 Version number 0.10.13: May 2017 release or later
Azure CLI v2 Version number 2.0.12: July 2017 release or later
AzCopy Version number 6.1.0: June 2017 release or later

Are P4 and P6 disk sizes supported for unmanaged disks or page blobs?

P4 (32 GiB) and P6 (64 GiB) disk sizes are not supported as the default disk tiers for unmanaged disks and page blobs. You need to explicitly set the Blob Tier to P4 and P6 to have your disk mapped to these tiers. If you deploy a unmanaged disk or page blob with the disk size or content length less than 32 GiB or between 32 GiB to 64 GiB without setting the Blob Tier, you will continue to land on P10 with 500 IOPS and 100 MiB/s and the mapped pricing tier.

If my existing premium managed disk less than 64 GiB was created before the small disk was enabled (around June 15, 2017), how is it billed?

Existing small premium disks less than 64 GiB continue to be billed according to the P10 pricing tier.

How can I switch the disk tier of small premium disks less than 64 GiB from P10 to P4 or P6?

You can take a snapshot of your small disks and then create a disk to automatically switch the pricing tier to P4 or P6 based on the provisioned size.

Can you resize existing Managed Disks from sizes less than 4 TiB to new newly introduced disk sizes up to 32 TiB?

New Managed Disk sizes 8 TiB, 16 TiB, and 32 TiB are currently in Preview. We don’t yet support resizing existing disk sizes to the new disk sizes.

What is the largest disk sizes supported by Azure Backup and Azure Site Recovery service?

The largest disk size supported by Azure Backup and Azure Site Recovery service is 4 TiB.

What are the recommended VM sizes for large disk sizes (>4TiB) for Standard SSD and Standard HDD disks to achieve optimized disk IOPS and Bandwidth?

To achieve the disk throughput of Standard SSD and Standard HDD large disk sizes (>4TB) beyond 500 IOPS and 60 MiB/s, you should use one of the following VM sizes to optimize your performance: B-series, DSv2-series, Dsv3-Series, ESv3-Series, Fs-series, Fsv2-series, M-series, GS-series, NCv2-series, NCv3-series, or Ls-Series VMs.

What regions are the managed disk sizes larger than 4 TiB supported in?

At this time in the preview, the managed disk sizes are supported in West US Central only.

Do we support enabling Host Caching on the newer disk sizes?

We support Host Caching of ReadOnly and Read/Write on disk sizes less than 4TiB. For disk sizes more than 4 TiB, we don’t support setting caching option other than None. We recommend leveraging caching for smaller disk sizes where you can expect to observe better performance boost with data cached to the VM.

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