SQL Server backup to URL fails if file exists

Question

I am attempting to backup a database to my Azure Blob storage. The databases are relatively large... between 1 and 30 Gig.

I have successfully backed up the first day, but on subsequent days, I get an error stating that the file already exists and that I need to use the WITH FORMAT.

But I need to do a differential backup, as the load of data on a full backup would be very slow and pricey.

I get the error "MyBackup.bak exists on the remote endpoint, and WITH FORMAT was not specified.".

What I am trying to do is:

BACKUP DATABASE [MyDatabase]' 
TO URL = 'https://myaccount.blob.core.windows.net/dbbackups/Container/', MyDatabase.bak', 
WITH CREDENTIAL = 'AzureDBBackupsContainer'
, DIFFERENTIAL
, COMPRESSION;

I have seen that a differential backup is supported when using URL backups.

Is this actually not possible, or am I doing something wrong?

Answer 1

It's correct in stopping you, because you need to keep the first full backup. When you restore your database, you will

• Restore from the full backup
• Apply the differential backup

Your script should generate a unique name. I do this by appending the date and time to the backup filename:

DECLARE
   @now DATETIME,
   @datePrefix VARCHAR(MAX),
   @timePart VARCHAR(MAX),
   @backupFileName VARCHAR(MAX),
   @fullUrl VARCHAR(MAX),
   @blobServiceEndpoint VARCHAR(MAX)

SET @now = GETDATE();
SET @datePrefix = CONVERT(VARCHAR(8), GETDATE(), 112);
SET @timePart = RIGHT('0' + CONVERT(VARCHAR(2), DATEPART(hh, @now)), 2) 
              + RIGHT('0' + CONVERT(VARCHAR(2), DATEPART(mi, @now)), 2)
              + RIGHT('0' + CONVERT(VARCHAR(2), DATEPART(ss, @now)), 2);
SET @backupFileName = 'MyDatabase_' + @datePrefix + @timePart + '.bak';
SET @blobServiceEndpoint = 'https://myaccount.blob.core.windows.net/';
SET @fullUrl = @blobServiceEndpoint + 'Container/' + @backupFileName;
BACKUP DATABASE [MyDatabase]' 
    TO URL = @fullUrl
    WITH CREDENTIAL = 'AzureDBBackupsContainer'
    , DIFFERENTIAL
    , COMPRESSION;