Andrew Hudson - Fedora™ Unleashed, 2008 edition

In this section, you learn about some of the most common backup hardware available and how to evaluate its appropriateness for your backup needs. With large storage devices becoming increasingly affordable (160GB IDE drives can be had for around $100) and prices falling on DVD recorders, decisions about backup hardware for the small business and home users have become more interesting.

Choosing the right media for you isn't as easy as it used to be back when floppy drives were the only choice. Today, most machines have CD-ROM drives that can read, but not write, CDs, which rules them out for backup purposes. Instead, USB hard drives and solid-state "pen" drives have taken over the niche previously held by floppy drives: you can get a 256MB drive for under $10, and you can even get capacities up to 16GB for good prices if you shop around. If your machine supports them (or if you have purchased a card reader), you can also use Compact Flash devices, which come in sizes up to 8GB in the Flash memory versions and 4GB for Hitachi Microdrives. Both USB hard drives and solid-state drives are highly portable. Support for these drives under Fedora is very good, accommodating these drives by emulating them as SCSI drives — the system usually sees them as /dev/scd1. Watch for improved support and ever-falling prices in the future. A 500GB USB hard drive costs about $150. The biggest benefits of USB drives are data transfer speed and portability.

FireWire (IEEE-1394) hard drives are similar to USB drives; they just use a different inter face to your computer. Many digital cameras and portable MP3 players use FireWire. Kernel support is available if you have this hardware. The cost of FireWire devices is now essentially zero, because many external drives come with both USB and FireWire as standard.

Compared to floppy drives and some removable drives, CD-RW drives and their cousins, DVD+RW/-RW drives, can store large amounts of data and are useful for a home or small business. Although very expensive in the past, CD writers and media are at commodity prices today, but automated CD changing machines, necessary for automatically backing up large amounts of data, are still quite costly. A benefit of CD and DVD storage over tape devices is that the archived uncompressed file system can be mounted and its files accessed randomly just like a hard drive (you do this when you create a data CD; refer to Chapter 7, "Multimedia"), making the recovery of individual files easier.

Each CD-RW disk can hold 650MB-700MB of data (the media comes in both capacities at roughly the same cost); larger chunks of data can be split to fit on multiple disks. Some backup programs support this method of storage. After it is burned and verified, the shelf life for the media is at least a decade or longer. Prices increase with writing speed, but a serviceable CD-RW drive can be purchased for less than $20.

DVD+RW/-RW is similar to CD-RW, but it is more expensive and can store up to 8GB of uncompressed data per disk. These drives sell for less than $50.

For network backup storage, remote arrays of hard drives provide one solution to data storage. With the declining cost of mass storage devices and the increasing need for larger storage space, network storage (NAS, or Network Attached Storage) is available and supported in Linux. These are cabinets full of hard drives and their associated controlling circuitry, as well as special software to manage all of it. These NAS systems are connected to the network and act as a huge (and expensive) mass storage device.

More modest and simple network storage can be done on a remote desktop-style machine that has adequate storage space (up to eight 250GB IDE drives is a lot of storage space, easily accomplished with off-the-shelf parts), but then that machine (and the local system administrator) has to deal with all the problems of backing up, preserving, and restoring its own data, doesn't it? Several hardware vendors offer such products in varying sizes.

Tape drives have been used in the computer industry from the beginning. Tape drive storage has been so prevalent in the industry that the tarcommand (the most commonly used command for archiving) is derived from the words Tape ARchive. Modern tape drives use tape cartridges that can hold 70GB of data (or more in compressed format). Capacities and durability of tapes vary from type to type and range from a few gigabytes to hundreds of gigabytes with commensurate increases in cost for the equipment and media. Autoloading tape-drive systems can accommodate archives that exceed the capacity of the file systems.

Older tape equipment is often available in the used equipment market and might be useful for smaller operations that have outgrown more limited backup device options.

Tape equipment is well supported in Linux and, when properly maintained, is extremely reliable. The tapes themselves are inexpensive, given their storage capacity and their opportunity for reuse. Be aware, however, that tapes do deteriorate over time and, being mechanical, tape drives can and will fail.

Neglecting to clean, align, and maintain tape drives puts your data at risk. The tapes themselves are also susceptible to mechanical wear and degradation. Hardware maintenance is part of a good backup policy. Do not ever forget that it is a question of when — not if — hardware will fail.

Because there are thousands of unique situations requiring as many unique backup solutions, it comes as no surprise that Linux offers many backup tools. Along with command-line tools such as tar and dd, Fedora also provides a graphical archiving tool, File Roller, that can create and extract files from archives. Finally, Fedora provides support for the Amanda backup application—a sophisticated backup application that works well over network connections and can be configured to automatically back up all the computers on your network. Amanda works with drives as well as tapes. The book Unix Backup and Recovery by W. Curtis Preston includes a whole chapter on setting up and using Amanda, and this chapter is available online at http://www.backupcentral.com/amanda.html.

The software in a backup system must support the hardware, and this relationship can determine which hardware or software choices you make. Many sysadmins choose a particular backup software not because they prefer it to other options, but because it supports the hardware they own.

The price seems right for free backup tools, but consider the software's ease of use and automation when assessing costs. If you must spend several hours implementing, debugging, documenting, and otherwise dealing with overly elaborate automation scripts, the real costs go up.

The tartool, the bewhiskered old man of archiving utilities, is installed by default. It is an excellent tool for saving entire directories full of files. For example, here is the command used to back up the /etcdirectory:

# tar cvf etc.tar /etc

Here, the options use tarto create an archive, are verbose in the message output, and use the filename etc.taras the archive name for the contents of the directory /etc.

Alternatively, if the output of taris sent to the standard output and redirected to a file, the command appears as follows: