SQL Server backup command can take backups in two or more split parts. By simply adding an additional DISK option we can split the files backup files.
BACKUP DATABASE AdventureWorks
TO DISK = 'C:\Backup\MultiFile\AdventureWorks1.bak',
DISK = 'C:\Backup\MultiFile\AdventureWorks2.bak',
DISK = 'C:\Backup\MultiFile\AdventureWorks3.bak'
GO
The backup is split into three equal parts of the original backup file size.
Restoring it is very similar – just add an additional DISK option.
RESTORE DATABASE [AdventureWorks]
FROM DISK = N'C:\Backup\MultiFile\AdventureWorks1.bak',
DISK = N'C:\Backup\MultiFile\AdventureWorks2.bak',
DISK = N'C:\Backup\MultiFile\AdventureWorks3.bak'
GO 
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