Data Backups and Disaster Recovery Planning

Data Backups and Disaster Recovery Planning Michelle M. Howell November 11, 2003 CS 5780 - Systems Administration University of Missouri at St. Louis

Introduction The collapse of the World Trade Center on September 11, 2001 reinforces the importance of backing up critical data, protecting the backups, and planning for disastrous data losses. It is estimated that the cost to replace technology and systems lost in the World Trade Center (WTC) disaster could be $3.2 billion (1). However, some companies that occupied the WTC, such as Morgan Stanley, were able to quickly recover. The financial giant was able to start running again because in addition to having the usual data backups that most companies keep on site, it also maintained real-time copies of its data in a second location miles away. All transactions occurring on the company WTC servers and mainframes were continuously transferred through high-speed telecommunications lines to computers in Teaneck, New Jersey. An event as unimaginable as the WTC collapse is not the only way to have a data loss disaster. There are countless ways to loose critical data. Human error is among the leading causes of data loss. For example, mistakes as simple as typing rm * at the UNIX command prompt can have disastrous results. In addition, software failure, hardware failure, computer viruses, malicious or disgruntled employees, and natural disasters such as fire and flood can cause a catastrophic system failure. The Disaster Recovery Institute International estimates that 90 percent of companies that experience a significant data loss are out of business within three years (2). Making backups of all data seems like the obvious solution. However, many small companies have inadequate backup practices or technology. The problem could be insufficient storage capacity, an inability to use backup solutions, a lack of backup testing, no offsite data storage, or inconsistent backup procedures. Unfortunately, backing up data is simply given a very low priority at a number of small firms. According to a survey conducted by storage media vendor Imation, 30% of small businesses lack formal data backup and storage procedures or do not implement those practices consistently. In fact, thirty-nine percent of the small firms surveyed admitted that they review their storage procedures only after a problem occurs. In addition, more than one third of the respondents said they do a fair or poor job of storing backup data offsite, and over half rate their disaster recovery plan as fair or poor (3). It is very difficult and in fact sometimes impossible to function normally during a crisis. It if for this reason that it is important to think about data backups before a disaster strikes. This paper provides some guidance for developing a data backup plan by summarizing data backup media and hardware technologies, data backup procedures and services, and data recovery services. It also provides an outline for disaster recovery planning. Data Backup Media and Hardware One of the first decisions to make when preparing a data backup plan is to decide what physical medium will be used to store the data backups. The speed, capacity, cost, and life expectancy of the medium are all considerations that should be taken into account when making this decision. 1

In terms of backup media life expectancy, a number of factors should be considered. For long term storage situations, the media may become obsolete due to changing technologies before it physically degrades. The information on this media would therefore become unusable. Similarly, the life expectancy of the media may be much longer than the amount of time it takes for the information on the media to degrade. Due to these considerations, care must be given when choosing media based on it s life expectancy. Hard Drives Data storage onto hard disk media is becoming more and more prevalent in corporate data centers, according to a survey of more than 1,000 information technology managers conducted by Peripheral Concepts, Inc. (4). Hard drives (magnetic disks) have a very high data capacity, currently holding over 100GB of data (5). A typical hard drive consists of platters that are coated with magnetic film. These platters spin while data is accessed by small heads situated on drive arms. This geometry enables data to be accessed randomly, and thus very quickly. In addition to a high storage capacity and speedy access, magnetic disks are estimated to have an expected life span of 5-10 years (6). Although hard disks used to be the most expensive backup media, prices have dropped exponentially in the last few years. Removable hard disks are becoming even more affordable, and have capacities of over 2GB. The Orb Drive, by Castlewood Corporation, is an example of such a product (7). Hard drives can be used for data backups by mirroring. Disk mirroring is a technique in which data is written to two duplicate disks simultaneously. If one of the disks fails, the system can quickly switch to the other disk without any loss of data or service. Mirroring is commonly used for systems such as Internet databases, where it is critical that data be accessible at all times. However, there is a problem with this technique: if both disks are a part of the same machine and the disk controller (or the whole machine) fails, neither disk would be accessible. One possible solution to this problem is to implement a mirroring scheme that involves multiple machines. The backup machine duplicates all of the processes of the primary machine. This is effective because if the primary machine fails, the backup machine can immediately take its place without any down time. Although this is a good solution for the problem of a failed machine, the possibility still exists for loss of both machines, for example due to fire. To prevent this situation, some companies have network mirroring. These companies mirror their main disks with disks in remote locations via a network connection. However, this type of mirroring is expensive. Each machine must be mirrored by an identical machine whose only purpose is to be there in the event of a failure. Of course, mirroring does not provide total protection against data loss. If a computer virus destroys files or files are accidentally deleted, the mirrored files will also be destroyed or deleted. Having a previously stored copy of the data is important, therefore traditional data backup media will still be required. The Peripheral Concepts survey (7) also shows that a large majority of data is still backed up and archived the traditional way: on tape. Magnetic tapes Magnetic tape is the most realistic and traditional medium for creating backups. The tape is actually a Mylar film strip on which information is magnetically stored. Because magnetic tapes 2

are a sequential storage device (tape drives cannot randomly access data like other storage devices, such as disk drives), they are much slower. However, high storage capacity and low cost make magnetic tapes the storage medium of choice for archiving large amounts of data. Helical scan devices are also magnetic tapes, but the data heads spin at an angle to the strip of tape, thus creating denser data storage and higher capacity. Life expectancy and the number of times a tape can be reused depends not only on the quality of the tape itself, but also the environment in which it is stored and the quality and maintenance of the tape drive heads. An estimate of magnetic tape life expectancy is 1 year (6). QIC (quarter inch cartridge, pronounced quick ) is a technology standard for magnetic tapes developed by a consortium of manufacturers called the Quarter-Inch Cartridge Drive Standards, Inc. (8). Travan tapes, developed by 3M Corporation, are a high density form of QIC standard tapes. Travan tapes were widely used by companies several years ago, but are now often used for personal computer backup Also called floppy tape because they can use a PC s floppy disk controller instead of requiring their own special controller, the drives are inexpensive and reliable. The current maximum storage capacity of Travan tapes is up to 10GB, but they are relatively slow. DAT (digital audio tape) come in two standard sizes, 8mm and 4mm. 4mm DAT's are helical scan devices and therefore can support storage capacities up to 20GB. 8mm DAT's have storage capacities of only about 7GB. The 4mm tapes have a great advantage over other tape media; they are physically the smallest and therefore take up less storage room. A disadvantage of these tapes is that they are very sensitive to heat damage, thus complicating the selection of a storage location. DAT tapes come in two formats. One format is for recording video or audio, the other is for binary data. The video/audio tapes work for making data backups, but they are less reliable than the binary format in terms of retaining data. The 4mm DAT is currently the most widely used tape type, but it is being replaced by digital linear tapes (DLT). DLT tapes have a storage capacity of up to 40GB. The drives are quite fast and are the newest standard backup media technology. Quantum Corporation (www.quantum.com), the manufacturer of the Super DLTtape II, claims a shelf life of 30 years on their product. Besides this unbeatable life expectancy, the DLT tape has another advantage. Like 4mm DAT s, DLT s are small. The DLT dimensions are approximately 1" X 4" X 4" and they weigh only about 8 ounces (9). DLT s are currently a very popular medium, even though they are still relatively expensive. Other Media Optical disks, such as recordable CD-RW s have a much longer lifespan than do tapes (except for DLT s). The estimated lifespan of optical media is greater than 30 years (6). However, optical disks have a smaller data capacity than tapes, and they are more expensive per GB. Floppy disks are the least expensive media, but because they have such a small capacity, a huge number of them are needed to back up even moderate amounts of data, thus making the price per GB very high. Table 1 summarizes the media types discussed above as well as several others. 3

Table 1. Comparison of backup media (10) Medium Capacity a Speed a Drive Media Cost/GB Reuse? Random Floppy disk 2.8MB < 100 KB/s $15 25 $91.43 Yes Yes SuperDisk 120MB 1.1 MB/s b $200 $8 $68.27 Yes Yes Zip 250 250MB 900 KB/s $200 $15 $61.44 Yes Yes CS-R 650MB 2.4 MB/s $200 75 $1.18 No Yes DC-RW 650MB 2.4 MB/s $200 $2 $3.15 Yes Yes Jaz 2GB 7.4 MB/s $350 $100 $50.00 Yes Yes Orb 2.2GB 12.2 MB/s b $200 $40 $18.18 Yes Yes Exabyte (8mm) 7GB 1 MB/s $1,200 $8 $1.14 Yes No Travan 10GB 1 MB/s $200 $34 $3.40 Yes No DDS-4 (4mm) 20GB 2.5 MB/s $1,000 $30 $1.50 Yes No ADR 25GB 2 MB/s $700 $40 $1.60 Yes No DLT (1/2 in.) 40GB 6 MB/s $4,000 $60 $1.50 Yes No AIT-2 (8mm) 50GB 6 MB/s $3,500 $95 $1.90 Yes No Mammoth-2 60GB 12 MB/s $3,500 $80 $1.33 Yes No a. Uncompressed capacity and speed b. Maximum burst transfer rate; the manufacturer does not disclose the true average throughput. Table 1 illustrates the problem with using inexpensive yet low capacity media such as floppy disks. Compare the cost per GB of floppy disks to DLT. Even though floppies and floppy drives are much less expensive than DLT cartridges and drives, they have such a small capacity that many more are needed to store data, thus resulting in a high cost per GB. The table also illustrates the differences in access speeds of the various storage media. For example, compare the speed of the Orb disk with the DLT speed. Orb is much faster because data is accessed randomly on disks, while tapes such as DLT require sequential access. Stackers, Autoloaders, and Tape Libraries As technology progresses and more work is becoming automated on a global scale, more and more data is being generated. Unfortunately, a decrease in human resources is happening concurrently. The result is that fewer people are available to handle data backups. What s more, due to this increase in data, stand-alone tape drives are often not sufficient in capacity to even backup mid-sized networks. A good solution to these problems is to automate backups. In addition to reducing the need for the manual handling of backup media, automated backups involve multi-volume media devices, thus greatly increasing storage capacity. Automation also makes backups reliable and consistent. Backup automation combines robotics with backup media and software to produce a device that can load, unload, and swap media without operator intervention. Stackers are tape changers that allow the operator to load a hopper with tapes. Tapes are inserted and removed in sequential order by the stacker s robotic mechanism. For a stacker to backup a filesystem, it would begin with the first tape and continue automatically inserting and removing tapes until the backup was complete or until it ran out of available cartridges. Autoloaders have the added functionality of 4

being able to provide any of their tapes upon request. Libraries are similar to autoloaders, but have the added ability to support larger scale backups, user initiated file recovery and simultaneous support of multiple users and hosts. Libraries are larger and more complex than stackers or autoloaders. As a result they are more expensive and tend to be used by larger scale companies. Tools for Backups and Backup Services Dump is the native UNIX utility that archives files to tapes. It is the most common way to create backups. Dump builds a list of files that have been modified since last dump, archives these files into a single file, and stores this file on an external device. Filesystems must be dumped individually. Dump works only on local machine, not over a network, so the dump command must be issued on each machine that is to be backed up. Note that the Solaris operating system s version of dump is not quite the same as other UNIX systems. In Solaris, the command ufsdump is equivalent to dump. Dump takes as an argument an integer value that represents a dump level. This is related to scheduling backups and is described in the next section, Scheduling Backup and Good Backup Practices. Free Tools AMANDA (The Advanced Maryland Automatic Network Disk Archiver) is a public domain utility developed by the University of Maryland. It was designed to backup many computers in a network onto a single server s high capacity tape drive. It also works with multiple stackers, allowing for a great increase in backup data capacity. AMANDA uses the native UNIX dump utility and does it's own dump level scheduling, given general information by the user about how much redundancy is desired in the data backups. AMANDA is one of the most popular free backup systems, and has a large user community. Based on the membership of AMANDArelated mailing lists, there are probably well over 1,500 sites using it (11). The UNIX System Administration Handbook (10) provides an abbreviated yet comprehensive walk-through of the AMANDA utility. BURT is a backup and recovery tool designed to perform backups to, and recoveries from, tapes. BURT is based on Tcl/Tk 8.0 scripts, and because of this it is very portable. It can backup multiple system platforms (12). The native UNIX dump utility can be automated with a shell script called hostdump.sh. Hostdump.sh enables the user to ensure that dump performed properly by checking return codes. It also provides an intelligent way to choose which filesystems to backup and creates a table of contents for each backup. Star is an implementation of the UNIX tar utility. It is the fastest known implementation of tar, with speeds exceeding 14MB/s (13). This is more than twice as fast as a simple dump. Another nice feature of Star is that it does not clobber files. More recent copies of files already on disk will not be overwritten by files from the backup medium during a restore. Star is available via anonymous ftp at ftp://ftp.berlios.de/pub/star. 5

Afbackup is a utility that was written and is maintained by Albert Flugel. It is a client/server backup system that allows many workstations to backup to a central server, either simultaneously or sequentially. The advantage of afbackup over a simple dump is that backups can be started remotely from the server or by cron scheduling on each of the clients. Bacula is a network based client/server backup program. It is a set of computer programs that manage backup, recovery, and verification of computer data across a network of different types of computer systems. Bacula is efficient and relatively easy to use, and offers many advanced storage management features that make it easy to find and recover lost or damaged files. Commercial Tools Makers of backup and recovery software booked $2.7 billion in revenues in 2001, and that figure is expected to grow to $4.7 billion in 2005, according to research firm IDC (14). This reflects the popularity of commercially available software for data backups. Legato and Veritas are currently two of the most popular backup software companies. NetWorker from Legato is a commercial package which allows storage devices to be placed throughout the network as NetWorker nodes. These nodes can then be managed during backups as if they are locally attached devices. The following is an excerpt from the Legato NetWorker Administrator s Guide, published on the website of Sun Microsystems (15): With NetWorker, you can: Perform automated lights out backups during non peak hours Administer, configure, monitor, and control NetWorker functions from any system on a network Centralize and automate data management tasks Increase backup performance by simultaneously sending more than one savestream to the same device Optimize performance using parallel savestreams to a single device, or to multiple devices or storage nodes NetWorker client/server technology uses the network protocol Remote Procedure Call (RPC) to back up data. The NetWorker server software consists of several server-side services and programs that oversee backup and recover processes. The NetWorker client software consists of client-side services and user interface programs. The server-side services and programs perform the following functions: Oversee backup and restore processes Maintain client configuration files Maintain an online client index Maintain an online media database NetBackup, available from Veritas Software Corporation, focuses on allowing users to back up data to disk and tape and to stage backups to disk for a period of time before moving them to 6

tape. This allows for faster data restores. NetBackup also features snapshot functionality which enables non-disruptive upgrades. In addition, NetBackup users can perform full system (baremetal) restorations of data to drives that do not contain an operating system. NetBackup also synchronizes laptop and desktop backup and restore operations with their server backups. Backup Services For most businesses, the standard recovery and backup solution hasn't changed for decades: tape. Every day, businesses back up every server to tape and then physically move those tapes offsite to a secure location for disaster protection. This increases the risk of human (tape mishandling) error. Another risk involved with this popular backup method is for the backups themselves to fail. Often it is not known that backups have failed until the data is needed for a recovery. To overcome these risks, businesses are beginning to use a new type of service, online server backup and recovery. There is currently a large selection of such service providers, but one good example is a popular company called LiveVault. LiveVault provides its customers with continuous online backup, recovery, and electronic vaulting (offsite storage). Companies that invest in such a service greatly decrease the risk of failed or neglected backups or data loss due to an onsite disaster. Another advantage of online backup and recovery is that because stored data does not reside directly on any of a network's servers, server power is utilized for business applications, and network capacity is released to the end user. Scheduling Backups and Good Backup Practices Creating a Backup Schedule There are two main categories of data backups: full backup and incremental backup. A full backup is a backup of every single file and folder within the source directory. The backup is therefore an exact copy of the source directory. This backup takes up as much disk space as the original (maybe a little less if compression is utilized). An incremental backup is a backup of only the changed files - files that have been added or modified since the last backup. Files that have been deleted since the last backup are also tracked. Incremental backups are defined by dump levels. As mentioned in an earlier section of this report, the UNIX dump command takes a dump level argument. The dump level is an integer in the range of 0 to 9. A level 0 dump backs up the entire file system while all other levels backup only those files that have been modified since the last dump of a level less than that level. The more frequently backups are done, the smaller the amount of data that can potentially be lost. Although it would seem that the simplest and safest solution to data backups would be to simply do a full backup every night, some additional factors must first be taken into consideration. Backups take time and personnel resources, and sometimes involve system disruption. Therefore, a company s backup schedule depends upon the need to minimize the number of tapes and the time available for doing backups. Additionally, the time available to do 7

a full restore of a damaged file system and the time available for retrieving individual files that are accidentally deleted need to be considered. If a company does not need to minimize the time and media spent on backups, it would be feasible to do full backups every day. However, this is not realistic for most sites, so incremental backups are used most often. An example of a moderate incremental backup schedule would be to back up enough data to restore any files from any day or week from the last month. This requires at least four sets of backup media one set for each week. These volumes could then be reused each month. In addition, each monthly backup would be archived for at least a year, with yearly backups being maintained for some number of years. This would enable the restoration of files from some month prior to the last month, at the expense of needing to restore from a tape which holds an entire month s worth of data. Similarly, data from some previous year could also be restored from one of the yearly tapes. Table 2 shows this incremental backup schedule. Table 2. Example cumulative weekly incremental backup schedule (16) Floating Mon Tues Wed Thurs Fri 1 st of Month 0 Week 1 9 9 9 9 3 Week 2 9 9 9 9 4 Week 3 9 9 9 9 5 Week 4 9 9 9 9 6 The numbers in Table 2 indicate the dump level used for that particular backup. All files that have changed since the lower level backup at the end of the previous week are saved each day. For each weekday level 9 backup, the previous Friday s backup is the closest backup at a lower level. Therefore, each weekday tape contains all the files changed since the end of the previous week (or the since the initial level 0 if it is the first week). For each Friday backup, the nearest lower-level backup is the previous Friday s backup (or the initial level 0 if it is the first Friday of the month). Therefore, each Friday's tape contains all the files changed during the week prior to that point. Please note that the choice of dump levels is arbitrary. For example, dump levels of all 7 or all 8 could have been used for the weekday backups. The choice of dump level relative to previous or subsequent dump levels it what is important. A detailed explanation of backup scheduling is provided in Unix Backup and Recovery (13). Good Backup Practices It is important to store data backups offsite, away from their source. Larry Ayoub, a senior executive at Bank of America, said, I think you have to accept that any data critical to the survival of a firm, or which the loss of would result in considerable financial or legal exposure, must be sent offsite in some manner, either physically or electronically (2). Forty-five percent of companies leave their server backup tapes onsite, vulnerable to natural calamities and security breaches, according to a recent survey from Massachusetts-based business continuity company, AmeriVault Corporation (2). Consider, for example, what would happen if data backups are stored in the back room of an office space. If the whole building were destroyed by a file, all data would have been unrecoverable. 8

Care should be given to the choice of backup location as well. For example, what might have happened if a company at the WTC had stored backups offsite by storing them on another floor in the WTC building? Even though the collapse of the WTC was an unimaginable event, businesses must prepare for the possibility of such events. Finding a good way to store backups is almost as important as setting up a schedule to create them. Backups should be stored in a place where only authorized people have access to them. A simple solution is to create copies on disk drives or tapes daily and then move them to an offsite location that is maintained by a data storage company. However, it can be difficult and expensive to move the media offsite. The best solution for offsite data storage is to instantaneously transfer data over network lines to a remote site. High security offsite backup services even mirror their data in offsite locations. Some additional considerations: Tapes should be labeled in a clear and consistent manner. In order to make restorations as painless as possible, backups need to be easy to get to and well labeled. Labeling includes clearly marking the tape itself as well as including a table of contents file so that individual files on the tape can be found easily. In sites where several people share responsibility for making backups or a number of different commands are used to create backups, the label should also include the command used to create the backup. The label is also an ideal place to keep a running tally of how many times the media has been used and how old it is. Backups must be tested regularly. Often, businesses have a good backup regimen with automated backup software and reliable media, yet they seldom test restores of their data. Backups can fail, and without testing the backups failure would not be detected until after a crisis occurs. Design data for backups keep filesystems to a size that is less than the backup media. This will greatly simplify backups and thus reduce the risk of error. Data Recovery The reason that so much planning and diligence must be devoted to data backups is to facilitate data recovery. Properly executed data backups will make the actual recovery of lost data the simplest task of all. After determining which volumes contain the data that needs to be recovered, data is simply recovered by using the native UNIX restore utility. The restore command is used to copy data from the volume to a selected directory on a selected filesystem. Note that the Solaris version of restore is actually ufsrestore. Details on the use of the restore command are provided in the UNIX System Administration Handbook (10). In some cases, a simple restore will not suffice. The data storage media may have physical damage. There are only two major companies in the United States who specialize in recovery of data from physical storage media. DriveSavers (www.driversivers.com) specializes in salvaging data damaged by fire, floods or hard-disk crashes. This company also maintains a museum of bizarre disk disasters on their website which is worth reading. Ontrack Data International 9

(www.ontrack.com) also offers a remote data recovery service for cases where the physical media is not destroyed. Disaster Recovery Plan For many companies, the most critical asset is their data. Implementing an effective data backup and recovery system ensures the protection of this data in most circumstances. However, catastrophic losses of entire systems (or worse, entire work sites) can and do happen. It is for this reason that companies must prepare for the worst by developing a disaster recovery plan. Although data backups and recovery are essential, they should not be thought of as disaster prevention, they should instead be considered a critical component of the disaster recovery plan. When preparing the plan, some considerations must be taken into account. A risk assessment must first be conducted. The risk assessment will help to determine how much data loss is acceptable. If it is not disastrous for a company to loose one day s worth of data, then it is not necessary to take data backups offsite every day. It is not desirable to spend too many resources getting backups offsite unnecessarily. However, if the daily data is critical, plans must be made for getting data offsite daily, or in some cases, more often. Documentation of the disaster recovery plan must be created. In addition to outlining the steps for recovering from a disaster, the documentation should provide contact information for software and hardware vendors as well as primary and secondary personnel who are familiar with the disaster recovery plan. Also, location of data backups should be identified. Because this document will guide the reader through the recovery process, it is essential that this document, like the company s data, be backed up and stored safely offsite. The final step to creating a disaster recovery plan is to test the plan. After the plan is in plan, it should be tested with regular audits that are done by third party companies. For example, a consultant could be hired someone who is competent and knowledgeable but unfamiliar with the system - to test the recovery system. This is necessary because those who are most familiar with the plan may not be available to implement it after a disaster. It is important that other personnel be able to understand and implement the plan. Conclusion Protection of a company s critical data is not only essential to its continued daily operations, it is also necessary for the survival of the company. Developing a strong data backup and recovery system is therefore essential. However, a data backup and recovery system is not the only element needed to protect a company s data. Disaster could strike a company s main systems at any time, and they need to be prepared to deal with it. That is why a comprehensive disaster recovery plan should be developed for any company that has data to protect. 10

References 1. Surette T., Genn V., Special Report - Disaster Recovery & Systems Backup. Australian Banking & Finance, Feb 28, 2002 v11 i3 p15. 2. Murray, Louise. Offsite storage: Sending your data away. SC Online Magazine, September 2003, http://www.scmagazine.com/scmagazine/2003_09/feature_4/4.html 3. Kovar, Joseph F. Precarious position CRN. Jericho, Sep 22, 2003, Iss. 1063; pg. 4A. Accessed online through ABI/INFORM Global Database, http://www.umsl.edu/services/library/ 4. Mearian, Lucas. Disk arrays gain in use for secondary storage: but tapes continue to handle most data for backups and archiving, survey finds. Computerworld, April 28, 2003 v37 i17 p12(1). Accessed online through ABI/INFORM Global Database, http://www.umsl.edu/services/library/ 5. IBM Corporation, Hard Disk Drives (HDD) Web Page, http://www.pc.ibm.com/ww/eserver/xseries/hdd.html, accessed November 3, 2003. 6. Indiana University, Storing Backups and Media Life Expectancy Web Page, http://www.ussg.iu.edu/usail/backups/storing/index.html, accessed November 3, 2003. 7. Castlewood Corporation, Home Page, http://www.castlewood.com/, accessed November 7, 2003. 8. Webopedia Online Dictionary for Computer and Internet Terms, http://www.webopedia.com/, copyright 2003. 9. Quantum Corporation, DLTtape Home Page, http://www.dlttape.com/home.htm, copyright 2003. 10. E. Nemeth, G. Snyder, S. Seebass, T.R. Hein. UNIX System Administration Handbook, Prentice Hall, 2001. 11. University of Maryland, AMANDA Web Page, http://www.amanda.org/, updated July 30, 2003. 12. Eric Melski, B.U.R.T. Backup and Recovery Tool Web Page, http://www.cs.wisc.edu/~jmelski/burt/, updated October 15, 1998. 13. Preston, Curtis. Unix Backup & Recovery. O Reilly & Associates, Inc., 1999. 14. Reuters, WTC Collapse Spotlights Need for Data Back-up, IEEE SPECTRUM Online, copyright 2001, http://www.spectrum.ieee.org/news/cache/onlinetechreport/09_12_2001.rittz1855-storybctechtechstoragedc.html. 15. Legato Systems, Inc., NetWorker Module for Informix Administrator s Guide Release 2.0, August 2000, http://www.sun.com/products-n-solutions/hardware/docs/pdf/875-1905-10.pdf. 16. Sun Microsystems, System Administration Guide, Volume 1, copyright 1994-2003, http://docs.sun.com/db/doc/805-7228/6j6q7uf0v 11