Evaluating Your Removable Media Needs

Fully understanding your needs can help lead you to a decision regarding the best type of removable disk to buy. In the end, you'll have to do some research on available media to determine which specific products will work best for you. Linux compatibility, described in the upcoming section, "Picking Linux-Compatible Hardware," is also a potential issue, although most removable-media devices work well with Linux. Some of the features you may want to consider include:

Capacity One of the most obvious factors is the capacity of the media. You may want to use two or three removable media devices in order to support multiple capacities.

Speed As a general rule, higher-capacity media produce faster speeds, but there are exceptions to this rule.

Interface Several methods of interfacing removable-media drives exist: floppy port, ATA, SCSI, USB, IEEE-1394, PC-card (most commonly used on laptops), and parallel port. As a general rule, ATA, SCSI, USB 2.0, and IEEE-1394 are the fastest and most reliable interface methods, although Linux IEEE-1394 support is not as mature as support for most other interfaces. Older USB 1 .x interfaces produce modest speed; they're fine for floppy disks, tape drives, and even Zip disks, but not for portable hard disks or 1GB or larger removable disks.

Internal versus External Devices that connect via the floppy or ATA ports are usually internal, although internal-to-external adapters are available. Most SCSI host adapters support both internal and external devices. The other interface methods all support external devices. External units are portable, so you can easily use them on multiple computers. External devices tend to be pricier than their internal counterparts, though, and they add to the cabling mess around your computer.

Media Durability For archival storage or if you move media around a lot, durability is important. CD-R and recordable DVD media are likely to be the most long-lasting, assuming they're properly stored. Estimates of their lifetimes range from 10 to 100 years. Floppies are notoriously unreliable as long-term storage media, and tapes aren't much better, although individual experiences differ substantially. Removable hard disks are sensitive to physical shocks, and so shouldn't be moved unnecessarily. For long-term storage, you may also want to consider the durability of the standard. For instance, CD-ROM and DVD-ROM drives are likely to be available for at least another decade or two, but less common and proprietary formats such as Castlewood Orb drives may not be.

Sequential versus Random Access Most removable media are random access devices, meaning that you can read data from any point on the medium without reading intervening data. You can write a normal Linux filesystem to such a device and treat it much as you would a hard disk. Tapes are sequential access devices, meaning that you must read all intervening data before reading the targeted data. This feature makes tapes a good choice for backups, but not for archives that should be random access.

Access Programs and Procedures Most media use ordinary Linux filesystem handling tools, such as the mount, umount, cp, and mv commands. CD-R and recordable DVD media require the use of special programs, such as cdrecord, to write data, but work with ordinary commands for reading data. This issue is described in the upcoming section, "Burning CD-Rs." Tapes also require special access methods. Typically, you use tar, dump, or some other tape backup tool to read and write tapes.

Cost Two costs are important to consider when choosing removable-media devices: the cost of the drive and the cost of the media. The total cost is the cost of the drive plus however many media you expect to need over its lifetime. You may want to consider both the absolute cost and the cost per megabyte or gigabyte stored. Because costs are constantly dropping, it's hard to summarize what's best in this arena, although CD-R drives and media are usually both well priced.

Table 2.5 summarizes some of the important characteristics of various popular removable media. Remember that these technologies keep improving, so you may find something with superior specifications to what's shown in Table 2.5.

Table 2.5: Characteristics of Popular Removable Media Technologies

Device Type

Capacity

Speed

Interfaces

Floppy Disk

180KB-2.88MB

Depends on capacity; typically 30KB/S

Floppy, USB

Iomega Zip Disk

100-750MB

0.6-2.4M B/s

ATA, SCSI, USB, parallel, PC-Card

LS-120 & LS-240

120-240MB

4.0MB/S

ATA, USB, parallel, PC-Card

Iomega Jaz

1-2GB

5.4MB/S

SCSI

Castlewood Orb

2.3-5.7GB

12.2—17.35MB/S

ATA, SCSI, USB, IEEE-1394

Magneto-Optical

128MB-9.1GB

2-6MB/S

SCSI

Iomega Peerless

5-20GB

15MB/S

IEEE-1394, USB

Removable Hard Disk

100MB-300GB

2-100MB/S

ATA, SCSI, IEEE-1394, USB

CD-R and CD-RW

700MB

150KB/S-7.5MB/S

ATA, SCSI, USB, IEEE-1394

Recordable DVD

4.7-9.4GB

4-8 M B/s

ATA, SCSI, IEEE-1394, USB 2.0

Tape

40MB-160GB

0.5-16M B/s

Floppy, ATA, SCSI, USB, parallel

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