Restoring a Microsoft SQL Server Database
This blog article is a scenario that I sent a coworker a while back about recovering a SQL Server database up to the point in time where a catastrophic hard disk drive failure occurs for the hard drive containing a SQL Server database. The transaction log for this database is on a separate physical disk and is still accessible.
I added the Northwind database to SQL Express on my machine, changed the recovery model to full, and then backed up the database and transaction log:
BACKUP DATABASE Northwind TO DISK = 'C:\Program Files\Microsoft SQL Server\MSSQL10.SQLEXPRESS\MSSQL\Backup\Northwind.bak'
WITH DESCRIPTION = 'Northwind Full Backup', NAME = 'Full Backup'
GO
BACKUP LOG Northwind TO DISK = 'C:\Program Files\Microsoft SQL Server\MSSQL10.SQLEXPRESS\MSSQL\Backup\Northwind1.trn'
WITH DESCRIPTION = 'Northwind Log Backup', NAME = 'Log Backup'
GO
Processed 392 pages for database ‘Northwind’, file ‘Northwind’ on file 1.
Processed 2 pages for database ‘Northwind’, file ‘Northwind_log’ on file 1.
BACKUP DATABASE successfully processed 394 pages in 0.922 seconds (3.331 MB/sec).
Processed 2 pages for database ‘Northwind’, file ‘Northwind_log’ on file 1.
BACKUP LOG successfully processed 2 pages in 0.074 seconds (0.171 MB/sec).
I modified a row of data:
UPDATE Categories
SET CategoryName = 'Drinks'
WHERE CategoryID = '1'
I stopped the SQL Server service and deleted the Northwind.mdf file and then restarted the SQL Server service, simulating a disk drive failure for the drive that contains the Northwind database. Keep in mind that the transaction log is on a separate physical disk.
I backed up the transaction log since it was still accessible:
BACKUP LOG Northwind TO DISK = 'C:\Program Files\Microsoft SQL Server\MSSQL10.SQLEXPRESS\MSSQL\Backup\Northwind2.trn'
WITH CONTINUE_AFTER_ERROR, DESCRIPTION = 'Northwind Log Backup - Tail', NAME = 'Log Backup'
Processed 9 pages for database ‘Northwind’, file ‘Northwind_log’ on file 1.
BACKUP LOG successfully processed 9 pages in 0.045 seconds (1.562 MB/sec).
I restored the database and applied all of the transaction log backups:
RESTORE DATABASE Northwind
FROM DISK = 'C:\Program Files\Microsoft SQL Server\MSSQL10.SQLEXPRESS\MSSQL\Backup\Northwind.bak'
WITH NORECOVERY
GO
RESTORE LOG Northwind
FROM DISK = 'C:\Program Files\Microsoft SQL Server\MSSQL10.SQLEXPRESS\MSSQL\Backup\Northwind1.trn'
WITH NORECOVERY
GO
RESTORE LOG Northwind
FROM DISK = 'C:\Program Files\Microsoft SQL Server\MSSQL10.SQLEXPRESS\MSSQL\Backup\Northwind2.trn'
WITH NORECOVERY
GO
RESTORE DATABASE Northwind WITH RECOVERY
GO
Processed 392 pages for database ‘Northwind’, file ‘Northwind’ on file 1.
Processed 2 pages for database ‘Northwind’, file ‘Northwind_log’ on file 1.
RESTORE DATABASE successfully processed 394 pages in 0.335 seconds (9.168 MB/sec).
Processed 0 pages for database ‘Northwind’, file ‘Northwind’ on file 1.
Processed 2 pages for database ‘Northwind’, file ‘Northwind_log’ on file 1.
RESTORE LOG successfully processed 2 pages in 0.012 seconds (1.057 MB/sec).
Processed 0 pages for database ‘Northwind’, file ‘Northwind’ on file 1.
Processed 9 pages for database ‘Northwind’, file ‘Northwind_log’ on file 1.
RESTORE LOG successfully processed 9 pages in 0.020 seconds (3.515 MB/sec).
RESTORE DATABASE successfully processed 0 pages in 0.512 seconds (0.000 MB/sec).
I validated my data changes which were only part of the transaction log backup that occurred after the simulated hard disk drive failure were restored to the database:
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