Frequently asked questions (FAQ) about Azure Files
Azure Files offers fully managed file shares in the cloud that are accessible via the industry-standard Server Message Block (SMB) protocol. You can mount Azure file shares concurrently on cloud or on-premises deployments of Windows, Linux, and macOS. You also can cache Azure file shares on Windows Server machines by using Azure File Sync for fast access close to where the data is used.
This article answers common questions about Azure Files features and functionality, including the use of Azure File Sync with Azure Files. If you don't see the answer to your question, you can contact us through the following channels (in escalating order):
- The comments section of this article.
- Azure Storage Forum.
- Azure Files UserVoice.
- Microsoft Support. To create a new support request, in the Azure portal, on the Help tab, select the Help + support button, and then select New support request.
How is Azure Files useful?
You can use Azure Files to create file shares in the cloud, without being responsible for managing the overhead of a physical server, device, or appliance. We do the monotonous work for you, including applying OS updates and replacing bad disks. To learn more about the scenarios that Azure Files can help you with, see Why Azure Files is useful.
What are different ways to access files in Azure Files?
You can mount the file share on your local machine by using the SMB 3.0 protocol, or you can use tools like Storage Explorer to access files in your file share. From your application, you can use storage client libraries, REST APIs, PowerShell, or Azure CLI to access your files in the Azure file share.
What is Azure File Sync?
You can use Azure File Sync to centralize your organization's file shares in Azure Files, while keeping the flexibility, performance, and compatibility of an on-premises file server. Azure File Sync transforms your Windows Server machines into a quick cache of your Azure file share. You can use any protocol that's available on Windows Server to access your data locally, including SMB, Network File System (NFS), and File Transfer Protocol Service (FTPS). You can have as many caches as you need across the world.
Why would I use an Azure file share versus Azure Blob storage for my data?
Azure Files and Azure Blob storage both offer ways to store large amounts of data in the cloud, but they are useful for slightly different purposes.
Azure Blob storage is useful for massive-scale, cloud-native applications that need to store unstructured data. To maximize performance and scale, Azure Blob storage is a simpler storage abstraction than a true file system. You can access Azure Blob storage only through REST-based client libraries (or directly through the REST-based protocol).
Azure Files is specifically a file system. Azure Files has all the file abstracts that you know and love from years of working with on-premises operating systems. Like Azure Blob storage, Azure Files offers a REST interface and REST-based client libraries. Unlike Azure Blob storage, Azure Files offers SMB access to Azure file shares. By using SMB, you can mount an Azure file share directly on Windows, Linux, or macOS, either on-premises or in cloud VMs, without writing any code or attaching any special drivers to the file system. You also can cache Azure file shares on on-premises file servers by using Azure File Sync for quick access, close to where the data is used.
For a more in-depth description on the differences between Azure Files and Azure Blob storage, see Deciding when to use Azure Blob storage, Azure Files, or Azure Disks. To learn more about Azure Blob storage, see Introduction to Blob storage.
Why would I use an Azure file share instead of Azure Disks?
A disk in Azure Disks is simply a disk. To get value from Azure Disks, you must attach a disk to a virtual machine that's running in Azure. Azure Disks can be used for everything that you would use a disk for on an on-premises server. You can use it as an OS system disk, as swap space for an OS, or as dedicated storage for an application. An interesting use for Azure Disks is to create a file server in the cloud to use in the same places where you might use an Azure file share. Deploying a file server in Azure Virtual Machines is a high-performance way to get file storage in Azure when you require deployment options that currently are not supported by Azure Files (such as NFS protocol support or premium storage).
However, running a file server with Azure Disks as back-end storage typically is much more expensive than using an Azure file share, for a few reasons. First, in addition to paying for disk storage, you also must pay for the expense of running one or more Azure VMs. Second, you also must manage the VMs that are used to run the file server. For example, you are responsible for OS upgrades. Finally, if you ultimately require data to be cached on-premises, it's up to you to set up and manage replication technologies, such as Distributed File System Replication (DFSR), to make that happen.
One approach to getting the best of both Azure Files and a file server that's hosted in Azure Virtual Machines (in addition to using Azure Disks as back-end storage) is to install Azure File Sync on a file server that's hosted on a cloud VM. If the Azure file share is in the same region as your file server, you can enable cloud tiering and set the volume of free space percentage to maximum (99%). This ensures minimal duplication of data. You also can use any applications you want with your file servers, like applications that require NFS protocol support.
For information about an option for setting up a high-performance and highly available file server in Azure, see Deploying IaaS VM guest clusters in Microsoft Azure. For a more in-depth description of the differences between Azure Files and Azure Disks, see Deciding when to use Azure Blob storage, Azure Files, or Azure Disks. To learn more about Azure Disks, see Azure Managed Disks overview.
How do I get started using Azure Files?
Getting started with Azure Files is easy. First, create a file share, and then mount it in your preferred operating system:
What storage redundancy options are supported by Azure Files?
Currently, Azure Files supports locally redundant storage (LRS), zone redundant storage (ZRS), and geo-redundant storage (GRS). We plan to support read-access geo-redundant (RA-GRS) storage in the future, but we don't have timelines to share at this time.
What storage tiers are supported in Azure Files?
Currently, Azure Files supports only the standard storage tier. We don't have timelines to share for premium storage and cool storage support at this time.
You cannot create Azure file shares from blob-only storage accounts or from premium storage accounts.
I really want to see a specific feature added to Azure Files. Can you add it?
The Azure Files team is interested in hearing any and all feedback you have about our service. Please vote on feature requests at Azure Files UserVoice! We're looking forward to delighting you with many new features.
Azure File Sync
What regions are supported for Azure File Sync?
The list of available regions can be found on the Region availability section of the Azure File Sync planning guide. We will continuously add support for additional regions, including non-Public regions.
Can I have domain-joined and non-domain-joined servers in the same sync group?
Yes. A sync group can contain server endpoints that have different Active Directory memberships, even if they are not domain-joined. Although this configuration technically works, we do not recommend this as a typical configuration because access control lists (ACLs) that are defined for files and folders on one server might not be able to be enforced by other servers in the sync group. For best results, we recommend syncing between servers that are in the same Active Directory forest, between servers that are in different Active Directory forests but which have established trust relationships, or between servers that are not in a domain. We recommend that you avoid using a mix of these configurations.
Changes made to the Azure file share by using the Azure portal or SMB are not immediately detected and replicated like changes to the server endpoint. Azure Files does not yet have change notifications or journaling, so there's no way to automatically initiate a sync session when files are changed. On Windows Server, Azure File Sync uses Windows USN journaling to automatically initiate a sync session when files change.
To detect changes to the Azure file share, Azure File Sync has a scheduled job called a change detection job. A change detection job enumerates every file in the file share, and then compares it to the sync version for that file. When the change detection job determines that files have changed, Azure File Sync initiates a sync session. The change detection job is initiated every 24 hours. Because the change detection job works by enumerating every file in the Azure file share, change detection takes longer in larger namespaces than in smaller namespaces. For large namespaces, it might take longer than once every 24 hours to determine which files have changed.
Note, changes made to an Azure file share using REST does not update the SMB last modified time and will not be seen as a change by sync.
We are exploring adding change detection for an Azure file share similar to USN for volumes on Windows Server. Help us prioritize this feature for future development by voting for it at Azure Files UserVoice.
If the same file is changed on two servers at approximately the same time, what happens?
Azure File Sync uses a simple conflict-resolution strategy: we keep both changes to files that are changed on two servers at the same time. The most recently written change keeps the original file name. The older file has the "source" machine and the conflict number appended to the name. It follows this taxonomy:
For example, the first conflict of CompanyReport.docx would become CompanyReport-CentralServer.docx if CentralServer is where the older write occurred. The second conflict would be named CompanyReport-CentralServer-1.docx.
Is geo-redundant storage supported for Azure File Sync?
Yes, Azure Files supports both locally redundant storage (LRS) and geo-redundant storage (GRS). If you initiate a storage account failover between paired regions from an account configured for GRS, Microsoft recommends that you treat the new region as a backup of data only. Azure File Sync does not automatically begin syncing with the new primary region.
Why doesn't the Size on disk property for a file match the Size property after using Azure File Sync?
See Understanding Cloud Tiering.
How can I tell whether a file has been tiered?
See Understanding Cloud Tiering.
A file I want to use has been tiered. How can I recall the file to disk to use it locally?
See Understanding Cloud Tiering.
How do I force a file or directory to be tiered?
See Understanding Cloud Tiering.
How is volume free space interpreted when I have multiple server endpoints on a volume?
See Understanding Cloud Tiering.
The following folders are also excluded by default:
\System Volume Information
Can I use Azure File Sync with either Windows Server 2008 R2, Linux, or my network-attached storage (NAS) device?
Currently, Azure File Sync supports only Windows Server 2019, Windows Server 2016, and Windows Server 2012 R2. At this time, we don't have any other plans we can share, but we're open to supporting additional platforms based on customer demand. Let us know at Azure Files UserVoice what platforms you would like us to support.
Why do tiered files exist outside of the server endpoint namespace?
Prior to Azure File Sync agent version 3, Azure File Sync blocked the move of tiered files outside the server endpoint but on the same volume as the server endpoint. Copy operations, moves of non-tiered files, and moves of tiered to other volumes were unaffected. The reason for this behavior was the implicit assumption that File Explorer and other Windows APIs have that move operations on the same volume are (nearly) instantaneous rename operations. This means moves will make File Explorer or other move methods (such as command line or PowerShell) appear unresponsive while Azure File Sync recalls the data from the cloud. Starting with Azure File Sync agent version 220.127.116.11, Azure File Sync will allow you to move a tiered file outside of the server endpoint. We avoid the negative effects previously mentioned by allowing the tiered file to exist as a tiered file outside of the server endpoint and then recalling the file in the background. This means that moves on the same volume are instantaneous, and we do all the work to recall the file to disk after the move has completed.
No: removing a server endpoint is not like rebooting a server! Removing and recreating the server endpoint is almost never an appropriate solution to fixing issues with sync, cloud tiering, or other aspects of Azure File Sync. Removing a server endpoint is a destructive operation, and may result in data loss in the case that tiered files exist outside of the server endpoint namespace (see Why do tiered files exist outside of the server endpoint namespace for more information) or in inaccessible files for tiered files existing within the server endpoint namespace. These issues will not resolve when the server endpoint is recreated. Tiered files may exist within your server endpoint namespace even if you never had cloud tiering enabled. We therefore recommend that you do not remove the server endpoint unless you would like to stop using Azure File Sync with this particular folder or have been explicitly instructed to do so by a Microsoft engineer. For more information on remove server endpoints, see Remove a server endpoint.
Can I move the storage sync service and/or storage account to a different resource group or subscription?
Yes, the storage sync service and/or storage account can be moved to a different resource group or subscription within the existing Azure AD tenant. If the storage account is moved, you need to give the Hybrid File Sync Service access to the storage account (see Ensure Azure File Sync has access to the storage account).
Azure File Sync does not support moving the subscription to a different Azure AD tenant.
NTFS ACLs carried from on-premises file servers are persisted by Azure File Sync as metadata. Azure Files does not support authentication with Azure AD credentials for access to file shares managed by the Azure File Sync service.
Security, authentication, and access control
Yes, Azure Files supports identity-based authentication and access control with Azure Active Directory (Azure AD) (Preview). Azure AD authentication over SMB for Azure Files leverages Azure Active Directory Domain Services to enable domain-joined VMs to access shares, directories, and files using Azure AD credentials. For more details, see Overview of Azure Active Directory authentication over SMB for Azure Files (Preview).
Azure Files offers two additional ways to manage access control:
You can use shared access signatures (SAS) to generate tokens that have specific permissions, and which are valid for a specified time interval. For example, you can generate a token with read-only access to a specific file that has a 10-minute expiry. Anyone who possesses the token while the token is valid has read-only access to that file for those 10 minutes. Currently, shared access signature keys are supported only via the REST API or in client libraries. You must mount the Azure file share over SMB by using the storage account keys.
Azure File Sync preserves and replicates all discretionary ACLs, or DACLs, (whether Active Directory-based or local) to all server endpoints that it syncs to. Because Windows Server can already authenticate with Active Directory, Azure File Sync is an effective stop-gap option until full support for Active Directory-based authentication and ACL support arrives.
The preview is available in all public regions.
No, Azure Files does not support authentication with Azure AD from on-premises machines in the preview release.
No, this scenario is not supported.
The preview release does not support REST APIs to get, set, or copy NTFS ACLs for directories or files.
If the subscription under which the file share is deployed is associated with the same Azure AD tenant as the Azure AD Domain Services deployment to which the VM is domain-joined, then you can then access Azure Files using the same Azure AD credentials. The limitation is imposed not on the subscription but on the associated Azure AD tenant.
No, Azure Files only supports Azure AD integration with an Azure AD tenant that resides in the same subscription as the file share. Only one subscription can be associated with an Azure AD tenant.
No, authentication from Linux VMs is not supported in the preview release.
No, Azure Files does not support preserving NTFS ACLs on file shares managed by Azure File Sync. The file ACLs carried from on-premises file servers are persisted by Azure File Sync. Any NTFS ACLs configured natively against Azure Files will be overwritten by the Azure File Sync service. Additionally, Azure Files does not support authentication with Azure AD credentials for access to file shares managed by the Azure File Sync service.
Yes. For more information see Azure Storage Service Encryption.
You can use shared access signatures to generate tokens that have specific permissions, and which are valid for a specified time interval. For example, you can generate a token that gives read-only access to a specific file, for a set period of time. Anyone who possesses the URL can access the file directly from any web browser while the token is valid. You can easily generate a shared access signature key from a UI like Storage Explorer.
If you mount the file share by using SMB, you don't have folder-level control over permissions. However, if you create a shared access signature by using the REST API or client libraries, you can specify read-only or write-only permissions on folders within the share.
Yes. Access to your Azure file share can be restricted at the storage account level. For more information, see Configure Azure Storage Firewalls and Virtual Networks.
Azure Files runs on top of the same storage architecture that's used in other storage services in Azure Storage. Azure Files applies the same data compliance policies that are used in other Azure storage services. For more information about Azure Storage data compliance, you can refer to Azure Storage compliance offerings, and go to the Microsoft Trust Center.
You can learn about various ways to workaround blocked port 445 here. Azure Files only allows connections using SMB 3.0 (with encryption support) from outside the region or datacenter. SMB 3.0 protocol has introduced many security features including channel encryption which is very secure to use over internet. However its possible that port 445 has been blocked due to historical reasons of vulnerabilities found in lower SMB versions. In ideal case, the port should be blocked for only for SMB 1.0 traffic and SMB 1.0 should be turned off on all clients.
No. ExpressRoute is not required to access an Azure file share. If you are mounting an Azure file share directly on-premises, all that's required is to have port 445 (TCP outbound) open for internet access (this is the port that SMB uses to communicate). If you're using Azure File Sync, all that's required is port 443 (TCP outbound) for HTTPS access (no SMB required). However, you can use ExpressRoute with either of these access options.
You can mount the file share by using the SMB protocol if port 445 (TCP outbound) is open and your client supports the SMB 3.0 protocol (for example, if you're using Windows 10 or Windows Server 2016). If port 445 is blocked by your organization's policy or by your ISP, you can use Azure File Sync to access your Azure file share.
How do I back up my Azure file share?
You can use periodic share snapshots for protection against accidental deletions. You also can use AzCopy, Robocopy, or a third-party backup tool that can back up a mounted file share. Azure Backup offers backup of Azure Files. Learn more about back up Azure file shares by Azure Backup.
Share snapshots: General
What are file share snapshots?
You can use Azure file share snapshots to create a read-only version of your file shares. You also can use Azure Files to copy an earlier version of your content back to the same share, to an alternate location in Azure, or on-premises for more modifications. To learn more about share snapshots, see the Share snapshot overview.
Are there limits on the number of share snapshots I can use?
Yes. Azure Files can retain a maximum of 200 share snapshots. Share snapshots do not count toward the share quota, so there is no per-share limit on the total space that's used by all the share snapshots. Storage account limits still apply. After 200 share snapshots, you must delete older snapshots to create new share snapshots.
How much do share snapshots cost?
Standard transaction and standard storage cost will apply to snapshot. Snapshots are incremental in nature. The base snapshot is the share itself. All the subsequent snapshots are incremental and will only store the diff from the previous snapshot. This means that the delta changes that will be seen in the bill will be minimal if your workload churn is minimal. See Pricing page for Standard Azure Files pricing information. Today the way to look at size consumed by share snapshot is by comparing the billed capacity with used capacity. We are working on tooling to improve the reporting.
Create share snapshots
Can I create share snapshot of individual files?
Share snapshots are created at the file share level. You can restore individual files from the file share snapshot, but you cannot create file-level share snapshots. However, if you have taken a share-level share snapshot and you want to list share snapshots where a specific file has changed, you can do this under Previous Versions on a Windows-mounted share.
If you need a file snapshot feature, let us know at Azure Files UserVoice.
Can I create share snapshots of an encrypted file share?
You can take a share snapshot of Azure file shares that have encryption at rest enabled. You can restore files from a share snapshot to an encrypted file share. If your share is encrypted, your share snapshot also is encrypted.
Are my share snapshots geo-redundant?
Share snapshots have the same redundancy as the Azure file share for which they were taken. If you have selected geo-redundant storage for your account, your share snapshot also is stored redundantly in the paired region.
Manage share snapshots
Restore data from share snapshots
Can I restore data from my share snapshot to a different storage account?
Yes. Files from a share snapshot can be copied to the original location or to an alternate location that includes either the same storage account or a different storage account, in either the same region or in different regions. You also can copy files to an on-premises location or to any other cloud.
Clean up share snapshots
Can I delete my share but not delete my share snapshots?
If you have active share snapshots on your share, you cannot delete your share. You can use an API to delete share snapshots, along with the share. You also can delete both the share snapshots and the share in the Azure portal.
Billing and pricing
Does the network traffic between an Azure VM and an Azure file share count as external bandwidth that is charged to the subscription?
If the file share and VM are in the same Azure region, there is no additional charge for the traffic between the file share and the VM. If the file share and the VM are in different regions, the traffic between them are charged as external bandwidth.
How much do share snapshots cost?
During preview, there is no charge for share snapshot capacity. Standard storage egress and transaction costs apply. After general availability, subscriptions will be charged for capacity and transactions on share snapshots.
Share snapshots are incremental in nature. The base share snapshot is the share itself. All subsequent share snapshots are incremental and store only the difference from the preceding share snapshot. You are billed only for the changed content. If you have a share with 100 GiB of data but only 5 GiB has changed since your last share snapshot, the share snapshot consumes only 5 additional GiB, and you are billed for 105 GiB. For more information about transaction and standard egress charges, see the Pricing page.
Scale and performance
What are the scale limits of Azure Files?
For information about scalability and performance targets for Azure Files, see Azure Files scalability and performance targets.
I need a larger file share than Azure Files currently offers. Can I increase the size of my Azure file share?
No. The maximum size of an Azure file share is 5 TiB. Currently, this is a hard limit that we cannot adjust. We are working on a solution to increase the share size to 100 TiB, but we don't have timelines to share at this time.
How many clients can access the same file simultaneously?
There is a quota of 2,000 open handles on a single file. When you have 2,000 open handles, an error message is displayed that says the quota is reached.
My performance is slow when I unzip files in Azure Files. What should I do?
To transfer large numbers of files to Azure Files, we recommend that you use AzCopy (for Windows; in preview for Linux and UNIX) or Azure PowerShell. These tools have been optimized for network transfer.
Why is my performance slow after I mount my Azure file share on Windows Server 2012 R2 or Windows 8.1?
There is a known issue when mounting an Azure file share on Windows Server 2012 R2 and Windows 8.1. The issue was patched in the April 2014 cumulative update for Windows 8.1 and Windows Server 2012 R2. For optimum performance, ensure that all instances of Windows Server 2012 R2 and Windows 8.1 have this patch applied. (You should always receive Windows patches through Windows Update.) For more information, see the associated Microsoft Knowledge Base article Slow performance when you access Azure Files from Windows 8.1 or Server 2012 R2.
Features and interoperability with other services
Can I use my Azure file share as a File Share Witness for my Windows Server Failover Cluster?
Currently, this configuration is not supported for an Azure file share. For more information about how to set this up for Azure Blob storage, see Deploy a Cloud Witness for a Failover Cluster.
Can I mount an Azure file share on an Azure Container instance?
Yes, Azure file shares are a good option when you want to persist information beyond the lifetime of a container instance. For more information, see Mount an Azure file share with Azure Container instances.
How do I use Azure Files with IBM MQ?
IBM has released a document that helps IBM MQ customers configure Azure Files with the IBM service. For more information, see How to set up an IBM MQ multi-instance queue manager with Microsoft Azure Files service.
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