UNIX System Administration Handbook - Evi Nemeth [110]
Super floppies
Iomega Zip drives are now ubiquitous, and they are often the default external medium on home PCs. The storage capacity of these drives has increased from 100MB to 250MB. The drives are available with parallel, serial, SCSI, and USB connectors.
Imation markets a SuperDisk product that can write both traditional floppy disks and special 120MB media.
Although these products are useful for exchanging data, their high media costs make them a poor choice for backups.
CD-R and CD-RW
The recent decreases in the price of recordable and read/write CDs makes them a far more attractive medium for backups than they were a few years ago. Both forms hold about 650MB. Drives that write these CDs are available in as many varieties as your favorite hard disk: SCSI, IDE, parallel, USB, etc.
CDs are written with a laser through a photochemical process. Although hard data has been elusive, it is widely believed that CDs have a substantially longer shelf life than magnetic media. Write-once CDs, known as CD-Rs, are not quite as durable as normal (stamped) CDs. CD-R is not a particularly good choice for normal backups, but it’s good for archiving data you might want to recover a long time in the future.
Recordable DVD technology is not yet widely available, but we look forward to its debut in the next couple of years. The capacity should be somewhere around 10GB.
Removable hard disks
A series of high-capacity removable disks have come onto the market over the last few years. Castlewood Industries has a 2.2GB product called an Orb drive. It comes in internal and external Ultra SCSI, EIDE, and USB varieties. For the gory details, see www.castlewood.com.
Another popular drive is the Iomega Jaz, which holds 2GB and claims an average transfer rate of 8.7 MB/s. The Jaz also claims a data shelf life of 10 years, whereas the Orb sets a more realistic target of 5 years. More information about the Jaz drive can be obtained from www.iomega.com.
The removable disk drive market is becoming very competitive, and prices vary daily. The main advantage of these products is speed: they achieve transfer rates comparable to normal disk drives. They are attractive as backup devices for small systems and home machines, although the disks themselves are somewhat pricey.
8mm cartridge tapes
Several brands of tape drive record to standard 8mm (small-format) videotapes. The drives are often referred to as “Exabytes drives,” after the first company that produced them. The original format held 2GB, and the newer formats hold up to 7GB. The hardware compression built into some drives pushes the capacity even higher.
The size of 8mm tapes makes off-site storage very convenient. Originally, the drive mechanisms were somewhat problematic in that they would fall out of alignment every 6-12 months and require a costly repair from the manufacturer. This is no longer the case.
8mm tapes come in both video and data grades. Some manufacturers insist on data grade and void your warranty if you use unapproved media. We have found video grade to be quite acceptable if it does not jeopardize the warranty. Be aware that both grades of tape are susceptible to heat damage.
DAT (4mm) cartridge tapes
DAT (Digital Audio Tape) drives are helical scan devices that use 4mm cartridges. Although these drives are usually referred to as DAT drives, they are really DDS (Digital Data Storage) drives; the exact distinction is unimportant. The original format held about 2GB, but successive generations have improved DDS’s capacity significantly. The current generation (DDS-4) holds up to 20GB.
DAT drives seek rapidly and transfer data at up to about 2.5 MB/s (for DDS-4), making the systems relatively fast. Their large capacity allows a complete backup to be performed without operator intervention at many sites. The 4mm tapes are compact, reducing the need for storage space and making off-site storage easy. DAT drives do not have a history of alignment