At the same time, new features from Microsoft, such as Volume Shadow Copy Service (VSS) and System Restore, make techniques more readily available.
The upshot is that you now have numerous choices when it comes to backup technologies.
Disk-based options: Mirroring, shadow copying and more
The most common type of backup activity is recovering corrupt or lost files and folders. New technologies have the most impact here. With disk-based technologies like mirroring, shadow copies, snapshots and incremental backups, you can keep up-to-date copies of files and restore them in minutes or seconds. In fact, in many cases the users can handle the job themselves.
Most of these techniques are varieties of replication -- meaning you end up with two distinct copies of the data. How they get there differs considerably.
The simplest technique, called mirroring, refers to making concurrent copies of data as it is created. It is fast, usually done locally, and requires twice the disk space for the same amount of data. Some systems use remote mirroring, in which case the data is mirrored somewhere else. It is more secure, but it is also more complex, since the characteristics of the link become important.
Most of the other techniques, such as Microsoft's Shadow Copy Services, don't store a complete second image of the data. Instead, they use various methods to reconstruct the data as it was at some point in time. Taking a snapshot of the data every so often is one way it's done, or simply backing up changes to the data incrementally. The results aren't as fast as reading off a local mirror, but they take up less disk space.
None of these approaches is a complete backup solution in itself. For one thing, a virus or other infector can easily propagate before it is noticed. For another, none of the methods provide secure, long-term storage for the data.
All of these techniques are disk-based and rely on large quantities of relatively inexpensive disk. They have become more popular as cost of disk storage has dropped and Serial ATA (SATA) disks have become available. SATA offers fast access combined with much lower cost than SCSI.
From hybrid solutions to blue laser DVDs
Increasingly, true backup is becoming a hybrid solution that combines disk and tape. The combination of shrinking backup windows and growing storage is pushing enterprises to use disk as an intermediary.
The role of backup is what it always has been -- true data protection. A well-designed backup system can completely restore your data even if a hurricane flattens your data center. This implies that at least one copy of all your data is stored off-site in a secure location.
Tape is still the mainstay, but now it is either combined with hard disks in disk-to-disk-to-tape (D2D2T) systems or it's being replaced entirely by disk storage. D2D2T is popular as a method of expanding the backup window shrunken by increasing data and 24-hour business cycles. The second set of disks serves to store the data for a short time, perhaps only a couple of hours, until it can be written to tape.
A few companies have dispensed with tape entirely and are backing up to a second or third set of disks, often at a remote location. This is practical if backing up is separate from archiving because data only remains on the backup disks for a month or two at most. Economically, a pure-disk backup is still generally more expensive than tape backup, but the differential isn't what it was even a couple of years ago.
DVD technology is having an impact on both backup and archival storage. With the proliferation of inexpensive DVD drives, many small organizations and individuals are using them. There are already a number of companies, such as JVC Americas Corp., that make DVD jukeboxes with capacities of up to 5.6 TB.
DVD storage should become more popular with large organizations in the next year as the next-generation blue laser products are released. Blue laser DVDs can store more than 25 GB per disk in the first generation, with at least 50 GB per disk promised for the next generation.
Change comes slowly for archival storage
The purpose of archived storage is to maintain long-term copies of information. The key concepts here are security and cost, with speed decidedly in third place. In some cases, acceptable access times can be measured in days, but in every case, the storage must be secure and it should be cheap. This is the classic "tapes-in-a-salt-mine" situation.
Archival storage has been changed the least by new storage methods. Although some companies now archive to optical drives, the vast majority still use tape combined with off-site storage, although this may change as optical storage becomes more developed. For example, Hitachi Maxell Ltd. has introduced a new line of DVD-Rpro disks that will probably outlast tape by a good margin. Long-life DVDs combined with blue laser technology will make optical storage much more attractive for archiving.
Rick Cook has been writing about mass storage since the days when the term meant an 80 K floppy disk. The computers he learned on used ferrite cores and magnetic drums. For the last 20 years he has been a freelance writer specializing in storage and other computer issues.