Database Reference
In-Depth Information
Figure
30-11
shows the content of the Azure Storage Container after a couple of database backups.
Figure 30-11.
Azure Storage Container
Each backup generates two files. One is the actual database backup, which could be compressed and encrypted
if needed. The other is the stab file that contains the metadata information about the backup.
Windows Azure blob storage is a cost-effective option for companies that want redundant storage for the
database backup files. However, this option is appropriate only for relatively static, non-mission critical databases
with RTOs that allow prolonged downtime. Neither the
BACKUP TO URL
command nor the Windows Azure Backup
Tool keeps a local copy of backup files. Therefore, it can take a lot of time to download backups in case of disaster.
Backing up large databases directly to the Cloud is also a questionable tactic, as it depends on the upload
bandwidth available. Uploading large, multi-gigabyte backup files can take hours or even days, which makes it
impractical.
With all being said, storing backup files on the Cloud can be a good option when you need a cost-effective,
redundant solution. Nonetheless, it is better to implement this separately from the SQL Server backup process,
uploading a local copy of the backup files afterwards. This approach allows you to recover a database quickly
from disaster using the local copy of the backup files while keeping another copy of the files on the Cloud for
redundancy purposes.
Finally, as of December 2013, both methods of database backup to Azure Blob Storage are limited to 1TB backup
size. This is more or less a theoretical limit at this point, as the main limitation is dictated by bandwidth rather than
file size.
Managed Backup to Windows Azure
SQL Server 2014 introduces the concept of Managed Backup to Windows Azure Blob Storage, which can be enabled
at the instance- or database-level. SQL Server automatically performs full and transaction log backups based on the
following criteria:
Full backup
is performed in any of the following situations: the last full backup was taken
more than a week previously, there is log growth of 1GB or more since the last full backup,
or the log chain is broken.
Transaction log backup
is taken every two hours, or when 5MB of log space is used.
Managed backup does not support databases in the SIMPLE recovery model, nor can it perform a differential
backup. Backup files can be retained in Azure Blob Storage for up to 30 days.
Managed backup backs up files to Windows Azure Blob Storage only. Local storage is not supported.
All considerations that we discussed in the
Backup to Windows Azure
section also apply to Managed backups.
