Magnetic tape has been the backup medium of choice for a long time. The advantage of tape is cost; it's less expensive than other storage options. However, the tradeoff is performance. As the amount of data that organizations have and need to back up has grown, the amount of time it takes to back up all that data to tape has become increasingly inconvenient. Likewise, finding data on tape is a time-consuming process. Consider music recorded to a cassette or reel-to-reel tape. To get to a song that's at the end of the tape, you have to fast forward through the entire tape. Compare this to a phonograph record or CD, where you can immediately start playing the disc at the place where the desired song is located.
A hard disk is read similarly to a phonograph record or CD; the drive heads can move immediately to the location on the disk where the desired data is stored. Writing to disk is also significantly faster than writing to a tape. Transfer speeds for fibre channel disks are at least three times faster than tape. And hard disk space has been getting less and less expensive, making it feasible to back up from disk to disk and do away with tape backups altogether. In fact, when you factor in the initial investment in the tape drive along with the tapes themselves and the lifespan of each type of media, as well as administrative overhead, you might find that disk to disk (D2D) backup is more cost effective than tape
Advantages of Disk Based Backup
Faster performance is one good reason to consider moving from tape to disk for your backups, but it's not the only reason. Anyone who's ever worked much with magnetic tape of any kind knows that it's fragile. Tape breaks, it's vulnerable to environmental factors such as humidity and heat, and it loses tension. Tape drive heads get dirty and have to be cleaned, and data isn't always restored perfectly due to these and other factors. Some experts estimate that from 25% to 50% of tape restorations fail, at least partially.
Disks are more durable than tape. They last longer, and they hold up under more frequent overwriting. Because they are contained inside sealed cases, there is less chance of the media being affected by the external environment. Of course, they never require retensioning or head cleaning.
Finally, disk backups are easier to manage. Keeping up with a collection of tape cartridges can become a logistical nightmare. Disk backup systems typically include management tools, often browser-based so you can easily configure settings and check status from anywhere.
Disk Based Backup Products
Sophisticated RAID array systems using fibre channel interfaces provide high capacity and fast throughput (for instance, Quantum's DX100 system will scale to 64TB with throughput of up to 2 TB per hour). Redundant RAID controllers, power supplies and fans provide extra protection for your data and dramatically increased reliability when compared to tape. Disk based systems can emulate a tape library so you don't have to change your current backup software; disk space appears to the backup software as virtual tape cartridges. Some backup programs give you the option of backing up to disk. The latest version of Veritas adds an "advanced disk based backup option" that allows you to restore data much more quickly than with traditional tape methods.
Software vendors are also making backup programs specifically for disk based systems. Some of these work on a client/server model. The client software is installed on the computers to be backed up and the server software creates a centralized "data repository" on the server. The software can encrypt the backup data for better security, and the data repository can be mirrored to another disk for added failsafe protection. Open file features allow you to back up databases and other files that are in use.
Hardware vendors are joining forces with software vendors to market disk based backup appliances. Cisco and EMC recently announced a collaborative effort aimed at producing an end-to-end storage consolidation solution that would provide backup of data from remote offices.
A Different Kind of Disk Based Alternative
Another way of backing up disk to disk is to back up your data to someone else's disk; that is, use an Internet based backup service and store your backed up data on the service's remote server. These services provide for easy off-site storage of your backup data, while it remains easily available when you need it. Companies that provide online backup services generally build multiple redundancies into their systems and often provide 24/7 staffing and monitoring. They often use "data vaults," so that your backed up information is physically secured within windowless rooms with reinforced concrete walls and redundant power supplies backed up by generators, to withstand natural disasters. Facilities are guarded and access is restricted, and the computer hardware is fault tolerant for minimal downtime. The better enterprise-level services provide Service Level Agreements that guarantee access availability.
Making Disk Based Backup Part of Your Backup Plan
You already have an investment in your current backup system (probably tape) and it may not be feasible or desirable to toss it out and replace it with all disk based backup. In fact, the two can be used together for a more effective backup solution. For example, you can use disk based software to back up data from your workstations and servers to a central repository, and then use the tape system on that server to provide a "backup of the backup."
For even more redundancy, you could also back up the repository data to an online service. Now you have on-site disk backup, a tape backup, and off-site backup in a hardened location. This might seem like overkill, but if your business depends on your data, multiple backups could be a lifesaver in the event of a catastrophe.
Of course, not all data is created equal, and you should evaluate the importance of different data and apply the appropriate measures to each type, based on the impact its loss would have on your business. It's worth going all out to protect your most mission critical data. For more information about taking this approach to backup, see Data Valuation - Rethinking "one size fits all" data protection at http://www.wwpi.com/Archive/show_article.asp?ArticleID=751.
The Future of Backup Technology
As new, faster and higher capacity storage solutions become available (and affordable), they will be utilized for backup purposes. InPhase Technologies recently demonstrated a prototype holographic drive and plans to start shipping it in 2006. Holographic drives can store data in three dimensions, and thus can potentially provide for a much larger capacity than current technologies. IBM and other companies are also working on holographic storage research.
Check out these companies for more information about their disk based backup solutions:
Backup For Workgroups: http://www.backup-for-workgroups.com
InPhase Technologies: http://www.inphase-technologies.com/
Backing up may be a hassle to do, but any business or individual who's ever lost important data knows how important it is. Today's huge data files and overall large volume of data that's produced can put a strain on traditional tape backup systems, which are slow, notoriously unreliable, and make it difficult to retrieve small amounts of data, such as a single lost file. Disk based backup is proving to be faster, less prone to failure and easier to manage. Consquently, it's gaining in popularity. You don't have to switch to disks all at once to enjoy its advantages, but we suspect that in the not-too-distant future, tape backups may be a thing of the past.