This is how I keep backup for seven days:

Use Master

Declare

@new_device nvarchar(40),

@new_file nvarchar(40),

@old_device nvarchar(40)

set @new_device='MyDB'+convert(char(8),getdate(),12)

set @new_file='d:\mssql\BACKUP\MyDB'+convert(char(8),getdate(),12)

set @old_device='MyDB'+convert(char(8),(getdate()-7),12)

EXEC sp_addumpdevice 'disk',@new_device,@new_file

BACKUP DATABASE MyDB TO @new_device

If exists (Select name from sysdevices

where name=@old_device)

EXEC sp_dropdevice @old_device,delfile