• Abstract and Figures
• Public Full-text

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).

Load more

  12

Copy Link