Restore fails with error "The media set has 2 media families but only 1 are provided. All members must be provided."

When you try to restore a backup, it might fail with the below error.

Msg 3132, Level 16, State 1, Line 1  The media set has 2 media families but only 1 are provided. All members must be provided.  Msg 3013, Level 16, State 1, Line 1  RESTORE DATABASE is terminating abnormally.

This means that the backup file provided for restore is not a complete one.

Okay, now what does "is not a complete one" mean?

This error pops up when the database is backed up into different files using the split backup technique.
In this case, the database backup was split into 2 files and while restoring the database only one file was mentions.
To fix this issue, you have to specify the complete list of backup files which were part of the backup procedure.

Split backups in SQL Server

Split backup is a method of performing the backups on a SQL Server database to multiple files.
When we perform the split backups on a database, the SQL server engine creates multiple backup files with the size split into the number of files mentioned in the backup command.

BACKUP DATABASE [SansSQL] TO  
 DISK = N'D:\Backup\SansSQL_Part1_Backup.bak' 
   ,DISK = N'D:\Backup\SansSQL_Part2_Backup.bak' 
WITH INIT, STATS = 10
GO

When you execute backup command like above then the backup of that particular database will be split into 2 different files of almost equal size.
This can be used with Full, Differential and Log backups as well.