|
The Problem with Tape Technology
Our DPM experts know that when it's time to go into disaster recovery mode, the tape backup system is often one of the biggest disasters. The traditional model of tape-based backup utilizing applications such as BackupExec and ARCserve is fraught with problems. Tape is slow, unreliable, and requires meticulous management. Microsoft's reported in-house operational experience indicates a 17% failure rate for its tape devices. Basically, for a tape-based restore procedure to be successful, too many things have to go right:
- IT managers need to have fast access to all the backup media required for a specific recovery
- All tapes must have no unreadable spots despite the fact that, in typical situations, they have been subject to physical wear by being rewritten many times
- Tapes must have been stored in the right environmental conditions to remain usable
- The software catalogs managing those tapes must not be corrupted
- Complex electromechanical tape drives must be available and working properly
The decisive disadvantage of tape as a backup-and-restore technology is that tape is slow. Tape backup typically calls for routinely scheduled system downtime, and tape-based recovery procedures can take intolerably long even when everything is working perfectly. Virtually all facets of contemporary businesses are becoming increasingly dependent on ready access to digital information, and the amount of data that companies generate to remain competitive is expanding dramatically. This growing reliance on networked data makes every minute of downtime more calamitous, while the ballooning volume of data being created adds steadily to the time required for tape-based backup and recovery.
Finally, tape-based backup and recovery regimes are logistically complex and demand substantial time and care to administrate. Media has to be managed, cataloged, and stored in a way that allows for consistent backup and accurate recovery, but issues such as personnel changes, company relocations, the need to accommodate remote offices, maintaining tape-friendly temperature and humidity in the storage facility, and the hassle of validation testing all invite human error or omission and inflate IT budgets. In essence, while tape technology remains a reasonable means of long-term archiving, it is becoming continually less viable as a technology for on-line backup and restoration.
Disk Drives to the Rescue
Microsoft Data Protection Manager radically changes the reliability and usability aspects of backup and restore. The key differentiator is that DPM is primarily an intelligent disk-to-disk based backup solution.
The basic concept is simple. You configure a DPM server with enough disk storage to hold a complete replica of all the data you want to protect from all your servers along with space for the historical changes you want to keep. For a 30-day history this may require somewhere in the range of 1.5 to two times the protected data space. The actual disk capacity needed is highly dependent on how often your data changes. Since disks are inexpensive and getting more affordable all the time, storage costs are relatively trivial for most IT organizations.
What is more significant is that a DPM server can be built with highly fault-tolerant components such as redundant power supplies and ample redundant cooling. By configuring RAID 5 or RAID 6 (double parity drives) striping on the backup disks, reliability is far higher than with tape-based systems.
Microsoft leveraged key technologies in Windows to make Data Protection Manager the backup-and-restore solution of choice. The foundation of DPM is the use of Volume Shadow Services for creating and maintaining extremely compact differentials. It does this both on the protected server for efficiently replicating change differentials over the network to the DPM server, but also on the DPM server itself for efficiently storing the historical snapshots used to recover data.
You can gain almost continuous data protection by replicating data from your protected servers as often as every 15 minutes. This means that if you have a failure on your server, in the worst case you can restore it to the last 15 minutes. This is far beyond the practical capability of tape-based backup systems. Basically, the DPM server always has a complete and up-to-date replica of all protected data. DPM takes further advantage of disk technology by storing the data in a Windows format file system that you can directly navigate to with Windows Explorer. DPM actually creates separate disk volumes for each protected server.
Thanks to support for disk-to-disk recovery and restore, DPM can reduce network recovery time from hours to minutes and make administrative tasks far more intuitive than with tape-based solutions. |