Lesson 1

In the best of circumstances, backups and archives will never be needed. However, data represents an investment of time and effort, and you should take measures to ensure your unique data against loss. Hard-drive failures, software bugs, and user errors can wreak havoc, deleting or corrupting important information. In mission-critical applications, lost or inaccessible data can mean the difference between meeting deadlines and satisfying customers or defaulting on a myriad of vital business responsibilities. Timely, consistent, and reliable backups are an extremely important aspect of system administration. In this module, you will learn how to protect your data using appropriate backup applications and scheduling. Additionally, you will use the file recovery facilities available in the tar utility and the restore command. Finally, you will learn about RAID: a) what RAID is, b) the different RAID levels, and c) the differences between hardware and software RAID.
Module Objectives After completing this module, you will be able to:

1. List the kinds of tape-drive hardware supported by Linux
2. Recognize tape control commands
3. Use the tar command to back up and restore files and directories
4. Use the dump command to back up file systems
5. Use the restore command to recover file systems
6. List tape backup applications available from Red Hat
7. Explain basic concepts related to RAID
8. Describe RAID levels
9. Compare and contrast hardware and software RAID

Armed with a backup strategy in mind, it is time to select a backup medium. Several types of backup hardware and media are available for use with Fedora and RHEL. Each type has its advantages and disadvantages.
The type of medium to choose depends largely on the amount of data you need to archive, how long you will store backups, how often you expect to recover data from your backups, and how much you can afford to spend. Table 4-1 compares the most common backup media. The following sections describe how to use magnetic tape, writable DVDs, and writable CDs as backup media.

Backup Medium	Advantages	Disadvantages
Magnetic tape	High capacity, low cost for archiving massive amounts of data.	Sequential access medium, so recovery of individual files can be slow.
Writable CDs	Random access medium, so recovery of individual files is easier. Backups can be restored from any CD-ROM drive.	Limited storage space (up to 700MB per CD).
Writable DVDs	Random access medium (such as CDs). Large capacity (4.7GB, although the actual capacity you can achieve might be less). DVD-R 9 and DVD-R 9 DVDs can store up to 8.5GB of data.	DVD-RW drives and DVD-R disks are relatively expensive (although they are coming down in price). As more manufacturers add DVD writers to their PCs, DVD will eventually replace CDs as the most common removable media drives.
Additional hard drive	Allows faster and more frequent backups. Fast recovery from crashes. No media to load. Data can be located and recovered more quickly. You can configure the second disk to be a virtual clone of the first disk, so that you can boot off of the second disk if the first disk crashes.	Data cannot be stored offsite; thus there is a risk of data loss if the entire server is destroyed. This method is not well suited to keeping historical archives of the many revisions of your files. The hard drive will eventually fill up. By using removable hard drives, you can overcome this limitation by removing the backup drive when it is full and moving it to a secure location.

The next lesson describes tape-drive hardware.