Limitations and known issues with SSH File Transfer Protocol (SFTP) support for Azure Blob Storage

บทความ
09/03/2024

This article describes limitations and known issues of SFTP support for Azure Blob Storage.

Important

Because you must enable hierarchical namespace for your account to use SFTP, all of the known issues that are described in the Known issues with Azure Data Lake Storage article also apply to your account.

Known unsupported clients

The following clients are known to be incompatible with SFTP for Azure Blob Storage. For more information, see Supported algorithms.

Kemp
paramiko 1.16.0
SSH.NET 2016.1.0

This list isn't exhaustive and might change over time.

Client settings

To transfer files to or from Azure Blob Storage via SFTP clients, see the following recommended settings.

WinSCP
- Under the Preferences dialog, under Transfer - Endurance, select Disable to disable the Enable transfer resume/transfer to temporary filename option.

Caution

Leaving this option enabled can cause failures or degraded performance during large file uploads.

Unsupported operations

Category	Unsupported operations
Random writes	Operations that include both READ and WRITE flags. For example: SSH.NET create API
Links	`symlink` - creating symbolic links `ln` - creating hard links Reading links not supported
Capacity Information	`df` - usage info for filesystem
Extensions	Unsupported extensions include but aren't limited to: fsync@openssh.com, limits@openssh.com, lsetstat@openssh.com, statvfs@openssh.com
SSH Commands	SFTP is the only supported subsystem. Shell requests after the completion of key exchange will fail.
Multi-protocol writes	Random writes and appends (`PutBlock`,`PutBlockList`, `GetBlockList`, `AppendBlock`, `AppendFile`) aren't allowed from other protocols (NFS, Blob REST, Data Lake Storage REST) on blobs that are created by using SFTP. Full overwrites are allowed.
Rename Operations	Rename operations where the target file name already exists is a protocol violation. Attempting such an operation returns an error. See Removing and Renaming Files for more information.
Cross Container Operations	Traversing between containers or performing operations on multiple containers from the same connection are unsupported.
Undelete	There is no way to restore a soft-deleted blob with SFTP. The `Undelete` REST API must be used.

Authentication and authorization

Local users are the only form of identity management that is currently supported for the SFTP endpoint.
Microsoft Entra ID isn't supported for the SFTP endpoint.

To learn more, see SFTP permission model and see Access control model in Azure Data Lake Storage.

Networking

To access the storage account using SFTP, your network must allow traffic on port 22.
Static IP addresses aren't supported for storage accounts. This isn't an SFTP specific limitation.
There's a 2-minute time out for idle or inactive connections. OpenSSH will appear to stop responding and then disconnect. Some clients reconnect automatically.

Other

For performance issues and considerations, see SSH File Transfer Protocol (SFTP) performance considerations in Azure Blob storage.
Resume and append operations require enabling the SFTP Resumable Uploads preview feature on your subscription. For more information on enabling preview features, see Set up preview features in Azure subscription.
By default, the Content-MD5 property of blobs that are uploaded by using SFTP are set to null. Therefore, if you want the Content-MD5 property of those blobs to contain an MD5 hash, your client must calculate that value, and then set the Content-MD5 property of the blob before the uploading the blob.
Maximum file upload size via the SFTP endpoint is 500 GB.
Customer-managed account failover is supported at the preview level in select regions. For more information, see Azure storage disaster recovery planning and failover.
To change the storage account's redundancy/replication settings, SFTP must be disabled. SFTP may be re-enabled once the conversion has completed.
Special containers such as $logs, $blobchangefeed, $root, $web aren't accessible via the SFTP endpoint.
Symbolic links aren't supported.
SSH and SCP commands that aren't SFTP aren't supported.
FTPS and FTP aren't supported.
TLS and SSL aren't related to SFTP.
Only SSH version 2 is supported.
Avoid blob or directory names that end with a dot (.), a forward slash (/), a backslash (), or a sequence or combination of the two. No path segments should end with a dot (.). For more information, see Naming and Referencing Containers, Blobs, and Metadata.

Blob Storage features

When you enable SFTP support, some Blob Storage features will be fully supported, but some features might be supported only at the preview level or not yet supported at all.

To see how each Blob Storage feature is supported in accounts that have SFTP support enabled, see Blob Storage feature support for Azure Storage accounts.

Troubleshooting

To resolve the Failed to update SFTP settings for account 'accountname'. Error: The value 'True' isn't allowed for property isSftpEnabled. error, ensure that the following prerequisites are met at the storage account level:
- The account needs to be a general-purpose v2 or premium block blob account.
- The account needs to have hierarchical namespace enabled on it.
To resolve the Home Directory not accessible error. error, check that:
- The user has been assigned appropriate permissions to the container.
- The container name is specified in the connection string for local users don't have a home directory.
- The container name is specified in the connection string for local users that have a home directory that doesn't exist.
To resolve the Received disconnect from XX.XXX.XX.XXX port 22:11: when connecting, check that:
- Public network access is Enabled from all networks or Enabled from selected virtual networks and IP addresses.
- The client IP address is allowed by the firewall.

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