|  | 8.1 | Basic Networking Knowledge
| 8.1.7 | Mirroring, duplexing, striping, volumes, tape backup
RAID Overview A technology called Redundant Array of Inexpensive Disks (RAID) was created to minimize the loss of data, should a system experience problems accessing data. RAID at each ot its levels defines performance, reliability, and cost. Mirroring RAID 1: Disk Mirroring is a common way to back up data. All information written to the first drive partition is also written to the mirror drive, making the two disk drives identical. A disk controller card connects to both the drives and writes the data in parallel to each of them. This single controller card creates a single point of failure for disk mirroring. An advantage is redundancy; however, disadvantages are cost and amount of disk space required. Duplexing RAID 1: Duplexing provides fault tolerance for both data and disk controller. In addition to disk mirroring, duplexing allows an additional controller connected to a driver. If one-controller fails, without duplexing the server would be down; however, duplexing provides a second controller and an intact configuration will still exist. The advantage of duplexing is that it is much faster than mirroring since the data can be written to both drives at the same time; while, the main disadvantage is the cost of the second controller card. Striping RAID 2: Striping data is a process where the data is spread out onto a number of disks. A minimum of three hard disks are needed, with three or more different drives sharing the data. With more than one disk sharing the data, the process makes the input/output (I/O) faster. Parity is also an option with data striping. Striping with parity works on RAID 5, which provides redundancy by interweaving data onto several drives and has a distributed checksum for parity. Volumes Volumes is a method, where there are at least two volumes on the server - on either the same physical disk or multiple disks. Normally, two volumes are used, a system volume and a data volume. The System volume holds all the operating system files, which allow the network to run. The data volume holds all of the varieties of user data. Because of volumes more physical disks can be added without administrative work being done to reorganize the logical structure of the storage. Tape Back Ups One of the oldest and cheapest ways to store data is by using a magnetic tape. There are three types of magnetic tapes that can be used to store data, Quarter Inch Tape (QIC), Digital Audio Tape (DAT), and Digital Linear Tapes (DLT). Quarter Inch Tape (QIC), which is rarely used nowadays, is used mostly for smaller networks and was one of the first standards used for PC backups. The earliest QIC had the ability to hold up to 40 megabytes of data; the most recent QIC has a capacity of up to 2 gigabytes. Digital Audio Tape (DAT), which was originally used for audio and video, provides digital recording for tape backups. DAT uses a SCSI connection and is used in most medium sized networks and has a maximum capacity of 24 gigabytes. Digital Linear Tapes (DLT), a form of tape backup that is becoming a more popular method, has the capacity of up to 80 gigabytes. Although this method is expensive, it is very fast and reliable. Like DAT, DLT uses a SCSI connection.
| Web Links
| CompTIA Home/Net + Certification
| Cisco Connection Online
| Cisco Documentation
| Search Cisco