Data is fragile. Backups are important. Before you select a strategy for protecting your data, you need to consider various disaster scenarios. Standard scenarios range from the loss of a user s key file to complete data erasure and computer damage from an electromagnetic pulse.
Your response depends on the computers that you need to protect. If you re a personal desktop user, most disasters are just an inconvenience. Chances are all you need to back up are files in your home directory. Backups of configuration files in /etc can save time as you reinstall and then reconfigure Linux. Administrators who are responsible for groups of computers need more complete backups. In some situations, you ll need media that you can access quickly, because information such as financial data can be time-sensitive.
Three different types of backups are available: full, incremental, and differential. Full backups are complete backups of all files on entire computer systems. Incremental backups include all data since the last full backup. Differential backups include all data since the last backup of any type.
There are wide varieties of media suitable for backups. The main candidates are tape drives and writeable CDs/DVDs. If an individual tape or CD does not provide enough room, devices such as jukeboxes are available that collect large numbers of tape drives or CDs/DVDs together in one backup computer.
For tapes and other media, you can use generic backup and restore commands such as tar , cpio , dump , and restore . If you re backing up to CDs or DVDs, you ll need to create an image of the files you want to save with the mkisofs command. Then you can write to the appropriate drive with the cdrecord or dvdrecord command.
One alternative to backups is RAID. A Redundant Array of Independent Disks provides data redundancy. In other words, if any single hard drive fails, the right type of RAID ensures that no data is lost. Red Hat Linux supports three types of RAID: RAID 0, which does not provide redundancy; RAID 1, which mirrors one hard disk onto another; and RAID 5, also known as striping with parity. Hardware RAID is available for this purpose.
In Red Hat Linux, you can create a software RAID array from a series of partitions, formatted to the Linux raid autodetect file type. Once you ve configured the device in /etc/raidtab , you can format and then mount your new RAID device. Just remember to label the partition with the e2label command. You also need to document that device in /etc/fstab , if you want Linux to mount it automatically the next time you boot.
Next, we ll look at Part IV , where we learn how to manage the X Window in Red Hat Linux. This starts in Chapter 15 with a detailed review of how to configure basic X Servers and X Clients. We ll examine configuration tools and the files they affect in detail. Then we ll look at how this can work for remote graphical applications.