Backing Up to a Hard Drive

As noted in the simple backup procedure in the beginning of this chapter, removable media such as tapes, DVDs, and CDs are not the only choice for backing up your data. You may find it useful to install a second hard drive in your system and use that drive for backups . This has several advantages over other backup media:

• Data can be backed up quickly and throughout the day; thus, backed-up data will be more current in the event of a crash.

• There's no medium to load. Data can be located and recovered more quickly.

• You can configure the second disk to be a virtual clone of the first one. If the first disk crashes, you can simply boot off of the second disk rather than installing new hardware. With disk mirroring software, this process can even be automated. The downside to this approach is that a mirrored drive that is online all the time is more prone to error than would be the case when copying files to (and removing) removable media.

• With new, cost-effective removable hard drives (including those connected via USB and FireWire), you have the convenience of removable media with what was once usually thought of as non-removable media.

There are some disadvantages to backing up to a hard drive. For example, the hard drive backup method is not well suited to keeping historical archives of the many revisions of your files, because the hard drive will eventually fill up. This problem can be reduced substantially, however, by using rsync snapshots, which store changes that are applied to modified files.

The simplest form of second-hard-drive backup is to simply copy important files to the other drive using the cp or tar command. The most sophisticated method is to provide fault-tolerant disk mirroring using RAID software.

A method in-between RAID and a simple cp command is to add an rsync command to a cron file, so that backups are done automatically as often as you please . For example, you could add a script that does your rsync backup to the /etc/cron.hourly , /etc/cron.daily ,/etc/cron.weekly , or /etc/cron.monthly , to have your backup run automatically each hour, day, week or month, respectively. Keep in mind that you would have to catch any problems within the set time frame (an hour , a day, and so on) before the bad data overwrites the backup. (I describe how to use the cron facility to do backups with dump later in this chapter.)