• Choose a category
• All
• Classic-Fiction

RAID level 0 RAID 0 is disk striping. It uses multiple drives and maps them together as a single physical drive. This is done primarily for performance, not for fault tolerance. If any drive in a RAID 0 array fails, the entire logical drive becomes unusable.

RAID level 1 RAID 1 is disk mirroring. Disk mirroring provides 100 percent redundancy because everything is stored on two disks. If one disk fails, another disk continues to operate. The failed disk can be replaced, and the RAID 1 array can be regenerated. This system offers the advantage of 100 percent data redundancy at the expense of doubling the storage requirements. Each drive keeps an exact copy of all information, which reduces the effective storage capability to 50 percent of the overall storage. Some implementations of disk mirroring are called disk duplexing (duplexing is a less commonly used term). The only difference between mirroring and duplexing is one more controller card. With mirroring, one controller card writes sequentially to each disk. With duplexing, the same data is written to both disks simultaneously. Disk duplexing has much faster write performance than disk mirroring. Many hardware implementations of RAID 1 are actually duplexing but they are still generally referred to as mirrors.

The data is intact in a RAID 1 array if either one of the two drives fails. After the failed drive is replaced with a new drive, you remirror the data from the good drive to the new drive to re-create the array.

RAID level 3 RAID 3 is disk striping with a parity disk. RAID 3 arrays implement fault tolerance by using striping (RAID 0) in conjunction with a separate disk that stores parity information. Parity information is a value based on the value of the data stored in each disk location. This system ensures that the data can be recovered in the event of a failure. The process of generating parity information uses the arithmetic value of the data binary. This process allows any single disk in the array to fail while the system continues to operate. The failed disk is removed, a new disk is installed, and the new drive is then regenerated using the parity information. RAID 3 is common in older systems, and it’s supported by most Unix systems.

RAID level 5 RAID 5 is disk striping with parity and is one of the most common forms of RAID in use today. It operates similarly to disk striping, as in RAID 0. The parity information is spread across all the disks in the array instead of being limited to a single disk, as in RAID 3. Most implementations require a minimum of three disks and support a maximum of 32.

These four types of RAID drives, or arrays, are illustrated in Figure 8.2.

FIGURE 8.2 The four primary RAID technologies used in systems

A RAID 5 array can survive the failure of any one drive and still be able to function. It can’t survive the failure of multiple drives.

You aren’t required to know the current RAID capabilities for the Security+ exam. They are presented here primarily for your knowledge. They are commonly used in highly reliable systems.

RAID levels 0, 1, 3, and 5 are the most commonly implemented in servers today. RAID 5 has largely replaced RAID 3 in newer systems.

RAID levels are implemented either in software on the host computer or in the disk controller hardware. A RAID hardware-device implementation will generally run faster than a software-oriented RAID implementation because the software implementation uses the system CPU and system resources. Hardware RAID devices generally have their own processors, and they appear to the operating system as a single device.

Real World Scenario

How Many Disks Does RAID Need?

As a security administrator, you must determine how many RAID disks you’ll need. Compute how many disks will be needed for each scenario or the amount of storage capacity you’ll end up with (answers appear at the end of each scenario).

Scenario 1 Your company has standardized on 500GB disks. A new server will go online next month to hold the data files