Backup Solutions Combining Disk and Tape
Updated: November 1, 2008
Applies To: System Center Data Protection Manager 2007
With DPM data protection, you can use disk-based storage, tape-based storage, or both.
Disk-based storage, also called D2D, for "disk-to-disk," is a type of backup in which data from one computer is stored on the hard disk of another computer. This contrasts with the more traditional method of backing up data from one computer to a storage media such as tape, also called D2T, for "disk-to-tape." For extra protection, the two methods can be combined in a disk-to-disk-to-tape (D2D2T) configuration that provides the rapid recovery benefits of disk-based storage in the short term and tape-based, archive storage for critical data in the long term. The following illustration shows the three storage methods.
Data Storage Methods
To determine which storage method to use, you must consider the relative importance of your organization's protection requirements.
How much data your organization can afford to lose. Realistically, not all data is equally valuable. Organizations must weigh the impact of loss against the costs of protection.
How quickly recovered data must be available. Recovery of data that is critical to ongoing operations is typically more urgent than routine data. On the other hand, organizations should identify servers providing essential services during working hours that must not be disrupted by recovery operations.
How long your organization must maintain data. Long-term storage might be necessary for business operations, depending on the type and contents of the data. An organization might also be subject to legal requirements for data retention, such as the Sarbanes-Oxley Act and the Data Retention Directive.
How much your organization can spend on data protection. When considering how much to invest in data protection, organizations must include the cost of hardware and media, as well as the personnel costs for administration, management, and support.
You can use DPM to back up data to both disk and tape, giving you the flexibility to create focused, detailed backup strategies that result in efficient and economic data protection. When you need to restore a single file or an entire server, recovery is fast and simple: you identify the data, and DPM locates the data and retrieves it (although your assistance might be needed if the tape has been removed from the library).
Disk-Based Protection and Recovery
One advantage of disk-based data protection is the potential time savings. Disk-based data protection requires none of the preparation time that tape-based protection does—locating the specific tape required for a job, loading the tape, positioning the tape to the correct starting point. The ease of using a disk encourages sending incremental data more frequently, which reduces the impact on the computer being protected and on network resources.
Data recovery with disk-based data protection is more reliable than that of tape-based systems. Disk drives typically have a much greater mean time between failure (MTBF) rating than tapes.
Recovery of data from disk is quicker and easier than recovery from tape. Recovering data from disk is a simple matter of browsing through previous versions of the data on the DPM server and copying selected versions directly to the protected computer. A typical file recovery from tape takes hours and can be costly, and administrators in a medium-size data center can usually expect to perform 10 to 20 or more of these recoveries each month.
Using DPM and disk-based data protection, data can be synchronized as frequently as every 15 minutes and maintained as long as 448 days.
Tape-Based Backup and Archive
Magnetic tape and similar storage media offer an inexpensive and portable form of data protection that is particularly useful for long-term storage.
In DPM, you can back up data from a computer directly to tape (D2T). You can also back up data from the disk-based replica (D2D2T). The advantage of creating your long-term backup on tape from the disk-based replica is that the backup operation can occur at any time with no impact on the computer being protected.
Additionally, a thorough disaster recovery plan includes offsite storage of critical information—you want to be able to recover your organization's data, should your facility be damaged or destroyed. Tape is a popular and convenient medium for offsite storage.
Using DPM, data can be backed up to tape as frequently as daily for short-term protection, and it can be maintained as long as 99 years for long-term protection.
By using software solutions from DPM partners, you can use removable media such as a USB hard drive in place of tape. For more information, see Data Protection Manager Partners (http://go.microsoft.com/fwlink/?LinkId=98869).