Ethernet Networking- P9

Ethernet Networking- P9:One of the biggest problems when discussing networking is knowing whereto start. The subject of computer networks is one of those areas for whichyou have to "know everything to do anything." Usually, the easiest way toease into the topic is to begin with some basic networking terminology andthen look at exactly what it means when we use the word Ethernet.
Nội dung trích xuất từ tài liệu:
Ethernet Networking- P9228 Security Issues How much should you back up? If you need to back up everything, then you do a full backup. Full backups ensure that the contents of the backup media are complete. Because the backup contains the most recent copy of each file, restoring from a full backup is also faster than any other type of restore. On the other hand, copying every file to backup media is the slow- est type of backup. You therefore might want an incremental backup, dur- ing which you copy only those files that have been changed since the last backup (archival or incremental). Because an incremental backup involves only a subset of the files, it can be performed much faster than a full back- up. However, restoring from incremental backups is more difficult because you must find the most recent copy of each file before restoring it. As files age and sit unused, you may decide that you no longer need them online. If you nonetheless need to retain the files (for legal or other rea- sons), then you will want to create an archival backup, during which you copy the files to some type of removable media and then delete them from online storage. The backup media are then stored in a safe place where they can be accessed if ever needed. How often should a backup be made? Perhaps you need a complete archi- val backup daily (or even more frequently), or perhaps you need an archi- val backup once a week, with incremental backups done daily. Given that it takes longer to recover from a set of incremental backups than from a single archival backup, but that making a complete archival backup takes longer than making incremental backups, what is the best mix of archiving and incremental backups for your organization? How quickly do you need to be back up and running after a system failure? How volatile are your files (how quickly do they change)? How much modified data are you will- ing to lose? Can you make backups while the network and/or servers are in use? Are there application programs that must be shut down to make backups of the data files they use? If you must bring some machines and/or applications off-line, when can you do so with minimal impact on your users? Who will perform the backups? Usually making backups is the responsi- bility of system operators, but you need to ensure that the backups are ac- tually being performed.Basic Defenses 229 How many generations of backups will you keep? Conventional wisdom states that you should keep three sets of backups, each one backup period older than the preceding. When time comes to create a fourth backup copy, you reuse the media from the oldest of the three existing backup copies. The idea is that if the first backup is damaged, you have two more to fall back to. The three-generation backup is good in theory, but beware: In some cases you can end up with all three backup copies being damaged. This is partic- ularly true if a system has been infected by a virus or worm that isnt de- tected immediately, or if a file is corrupted by being written to a bad disk sector or some other similar problem. (You wont detect the latter until someone attempts to read the file, by which time it may be too late to re- cover a clean copy of the file.) Where will you store the backups? Its convenient to have the backups close at hand--somewhere on s i t e ~ b u t if your physical facility is dam- aged, your backup media might be damaged as well. Therefore, you prob- ably want to keep at least one backup copy offsite. Which site will you use? Do you want to pay simply for offsite storage, or do you want a true hot site, where you can run your software until your facility is restored? A good storage site is secure from environmental extremes (heat, cold, fire, and water) and is easily and readily accessible. You will need 24/7 access to your offsite backups, in all kinds of weather. A mountain-top cave may be cool and dry and safe from flooding, but it could be too hard to reach in the winter.Backup Media During the period when your files were so small they would fit on a single floppy disk, choosing backup media was easy. Floppies were cheap and ...