A SQL Server backup file is written by the Database Engine service, even when a maintenance plan is launched by SQL Server Agent. Grant the engine service identity write access to both the SMB share and its filesystem folder, then use a UNC path rather than a mapped drive.
Last updated: October 9, 2026.
BACKUP DATABASE Sales
TO DISK = N'\backup01sqlbackupsSalesSales_full.bak'
WITH CHECKSUM,
COMPRESSION,
INIT,
STATS = 10;
GO
RESTORE VERIFYONLY
FROM DISK = N'\backup01sqlbackupsSalesSales_full.bak'
WITH CHECKSUM;
GOCreate the destination directory in advance and verify effective permissions for the exact service identity. A successful interactive file copy proves only that your signed-in Windows account has access; SQL Server runs in a different security context. Test a small database directly before adding the operation to a maintenance plan.
Grant access to the identity that opens the backup file
Find the SQL Server Database Engine account in SQL Server Configuration Manager. For a domain service account or group managed service account, grant that identity the necessary share and NTFS permissions. If the engine runs as a virtual or network service account, remote access commonly uses the database server computer account, such as DOMAIN\SQLHOST$.
Microsoft’s backup-device documentation states that the SQL Server service account needs access to a remote share and recommends a fully qualified UNC name.
Why an Agent proxy may not solve the backup task
A maintenance-plan package can run under a SQL Server Agent proxy, but the BACKUP DATABASE operation still asks the Database Engine to create the file. Changing only the SSIS proxy credential therefore may leave the actual writer without access. Microsoft’s backup troubleshooting guide confirms that backup statements run under the Database Engine startup account.
Avoid drive letters because Windows services do not inherit your interactive mapped drives. After the backup, perform restore testing in addition to VERIFYONLY. Continue with backup access troubleshooting, backup verification, and restoring on another server.
