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6. Media Size
Tape has an almost unlimited media size because of the ability to span huge backups across multiple tapes. The other buzzworthy term for this phenomenon is "scalability." Tape has an almost infinitely scalable design. You can backup an entire data center with tape. Then you can do it again tomorrow, the next day and so on.
Tape is a reliable media, even under extreme conditions. If a tape cassette fails, you can salvage the data by winding the tape onto an empty cassette. Tape drives are extremely reliable and able to operate with thousands of hours between failures. Most failures are mechanical problems with the drive mechanisms and not with the media. Tape drive reliability (250,000+ hours MTBF) is difficult, if not impossible, to replicate with spinning disks because storage media and the mechanical drive are separate entities. Your tape drive might fail, but chances are slim your data will go with it. Data that resides on disks, however, is not so lucky.
8. Power Consumption
Tape drive power consumption is very low on a per-gigabyte (GB) or per-terabyte (TB) level. The average power consumption for a Quantum LTO04HH Model B drive is 20 Watts. The new 'green' disk drives consume approximately 5 Watts each. It doesn't take a mathematical genius to realize how much required power you'll need to build an equivalent tape replacement system with disks.
Tape drives perform at very high speeds (for tape) in the range of 30 to 80MB/sec sustained and bursts to 300+MB/sec. At these speeds, offloading data to tape still makes sense for the largest enterprises. No, tape doesn't break any speed records, but for offloading from VTLs, speed is not a major concern.
Backup automation is a huge advantage of tape backup for enterprises. Using autoloaders, tape backup systems can run continuously, which means backups may run with minimal human intervention. Automated media exchange is a labor saver that keeps backup operations running smoothly.
Ken Hess is a freelance writer who writes on a variety of open source topics including Linux, databases, and virtualization. He is also the coauthor of Practical Virtualization Solutions, which was published in October 2009. You may reach him through his web site at http://www.kenhess.com.