Books bearing O'Reilly's name and trademark cover images almost never fail to live up to the standard of quality this publisher repeatedly strives to reach. -- Kerri-Leigh Grady, CompuNotes, Feb 2003
I'm delighted to say it's already earned a place on my 'most-used' pile. -- StudioB.com, October 8, 2002
She didn't just jam the book with dry, technical facts, but included pertinent, humorous, anecdotes that always underscored the topic at hand. -- Matthew Cheek, UnixReview, Nov 28, 2002
This is the definitive guide for system administrators. -- WebReference.com, Oct 3, 2002
From the Publisher
About the Author
Æleen Frisch has been a system administrator for over 20 years, tending a plethora of VMS, Unix, and Windows systems over the years. Her current system administration responsibilities center on looking after a very heterogeneous network of Unix and Windows NT/2000/XP systems. She is also a writer, lecturer, teacher, marketing consultant and occasional database programmer. She has written eight books, including Essential System Administration (now in its third edition), Essential Windows NT System Administration and the Windows 2000 Desktop Reference (all from O'Reilly Media, Inc.) and Exploring Chemistry with Electronic Structure Methods (Gaussian, Inc.). Currently, she writes the "Guru Guidance" column for Linux Magazine. She also writes poetry and is currently working on her first novel.
Excerpt. © Reprinted by permission. All rights reserved.
Every user of any computer figures out sooner or later that files are occasionally lost. These losses have many causes:users may delete their own files accidentally, a bug can cause a program to corrupt its data file,a hardware failure may ruin an entire disk,and so on.The damage resulting from these losses can range from minor to expansive and can be very time-consuming to fix.To ensure against loss,one primary responsibility of a system administrator is planning and implementing a backup system that periodically copies all files on the system to some other location.
It i also the administrator s responsibility to see that backups are performed in a timely manner and that backup tapes (and other media)are stored safely and securely.This chapter will begin by discussing backup strategies and options and then turn to the tools that Unix systems provide for making them.
An excellent reference work about backups on Unix systems is Unix Backup and Recovery by W.Curtis Preston (O Reilly &Associates).It covers the topics we are discussing here in complete detail and also covers material beyond the scope of this book (e.g.,backing up and restoring databases).
Planning for Disasters and Everyday Needs
Developing an effective backup strategy is an ongoing process.You usually inherit something when you take over an existing system and start out doing the same thing youve always done when you get a new system.This may work for a while,but Ive seen companies try to retain their centralized,hordes-of-operators based backup policies after they switched from a computer room full of mainframes to a building full of workstations. Such an attempt is ultimately as comical as it is heroic,but it all too often ends up only in despair,with no viable policy ever replacing the outdated one.The time to develop a good backup strategy is right now,starting from however you are approaching things at the moment.
Basically,backups are insurance.They represent time expended in an effort to prevent future losses.The time required for any backup strategy must be weighed against the decrease in productivity,schedule slippage,and so on if the files are needed but are not available.The overall requirement of any backup plan is that it be able to restore the entire system or group of systems within an acceptable amount of time in the event of a large-scale failure.At the same time,a backup plan should not sacrifice too much in the way of convenience,either in what it takes to get the backup done or how easy it is to restore one or two files when a user deletes them accidentally.The approaches one might take when considering only disaster recovery or only day-to-day convenience in isolation are often very different,and the final backup plan will need to take both of them into account (and will accordingly reflect the tension between them).
There are many factors to consider in developing a backup plan.The following questions are among the most important:
What files need to be backed up?The simplest answer is,of course,everything ,and while everything but scratch files and directories needs to be saved somewhere, it doesn t all have to be saved as part of the system backups.For example,when the operating system has been delivered on CD-ROM,there is really no need to back up the system files,although you may choose do so anyway for reasons of convenience.
Where are these files?This question involves both where the important files are within the filesystem and which systems hold the most important data.
Who will back up the files?The answer may depend on where the files are.For example, many sites assign the backup responsibility for server systems to the system administrator(s) but make users responsible for files that they keep on their workstations local disks.This may or may not be a good idea,depending on whether or not all of the important files really get backed up.
Where,when,and under what conditions should backups be performed?Where refers to the computer system on which the backup will be performed;this need not necessarily be the same as the system where the files are physically located. Similarly,in an ideal world,all backups would be performed after hours on unmounted filesystems.Thats not always practical in the real world,however.
How often do these files change?This information will help you decide both when and how often to perform backups and the type of schedule to implement. For example,if your system supports a large,ongoing development project,the files on it are likely to change very frequently and will need to be backed up at least daily and probably after hours.On the other hand,if the only volatile file on your system is a large database,its filesystem might need to backed up several times every day while the other filesystems on the same system would be backed up only once a week.*
*In actual fact,a database is often backed up using a facility provided by the software vendor,but you get the idea here.
How quickly does an important missing or damaged file need to be restored?Since backups protect against both widespread and isolated file loss,the timeframe in which key files need to be back online needs to be taken into account.The number of key files, how widely spread they are throughout a filesystem (or network),and how large they are will also influence matters.Your system may only have one irreplaceable file,but you ll need to plan very differently depending on whether it is 1 KB or 1 GB in size.Note that losing even a single 1 KB file can wreak havoc if it s the license file without which the central application program wont run.