Administrators often upgrade disk subsystems to improve their performance and redundancy. If you’re planning to take the SY0-501 version of the Security+ exam, you should understand how resiliency and automation strategies reduce risk.
For example, can you answer this question?
Q. You are a technician at a small organization. You need to add fault-tolerance capabilities within the business to increase the availability of data. However, you need to keep costs as low as possible. Which of the following is the BEST choice to meet these needs?
A. Alternate processing site
B. RAID-10
C. Backups
D. Faraday cage
More, do you know why the correct answer is correct and the incorrect answers are incorrect? The answer and explanation are available at the end of this post.
Disk Redundancies
Any system has four primary resources: processor, memory, disk, and the network interface. Of these, the disk is the slowest and most susceptible to failure. Because of this, administrators often upgrade disk subsystems to improve their performance and redundancy.
Redundant array of inexpensive disks (RAID) subsystems provide fault tolerance for disks and increase the system availability. Even if a disk fails, most RAID subsystems can tolerate the failure and the system will continue to operate. RAID systems are becoming much more affordable as the price of drives steadily falls and disk capacity steadily increases. While it’s expected that you are familiar with RAID subsystems, the following provides a short summary to remind you of the important details.
RAID-0
RAID-0 (striping) is somewhat of a misnomer because it doesn’t provide any redundancy or fault tolerance. It includes two or more physical disks. Files stored on a RAID-0 array are spread across each of the disks.
The benefit of a RAID-0 is increased read and write performance. Because a file is spread across multiple physical disks, the different parts of the file can be read from or written to each of the disks at the same time. If you have three 500 GB drives used in a RAID-0, you have 1,500 GB (1.5 TB) of storage space.
RAID-1
RAID-1 (mirroring) uses two disks. Data written to one disk is also written to the other disk. If one of the disks fails, the other disk still has all the data, so the system can continue to operate without any data loss. With this in mind, if you mirror all the drives in a system, you can actually lose half of the drives and continue to operate.
You can add an additional disk controller to a RAID-1 configuration to remove the disk controller as a single point of failure. In other words, each of the disks also has its own disk controller. Adding a second disk controller to a mirror is called disk duplexing.
If you have two 500 GB drives used in a RAID-1, you have 500 GB of storage space. The other 500 GB of storage space is dedicated to the fault-tolerant, mirrored volume.
RAID-2, RAID 3, and RAID-4 are rarely used.
RAID-5 and RAID-6
A RAID-5 is three or more disks that are striped together similar to RAID-0. However, the equivalent of one drive includes parity information. This parity information is striped across each of the drives in a RAID-5 and is used for fault tolerance. If one of the drives fails, the system can read the information on the remaining drives and determine what the actual data should be. If two of the drives fail in a RAID-5, the data is lost.
RAID-6 is an extension of RAID-5, and it includes an additional parity block. A huge benefit is that the RAID-6 disk subsystem will continue to operate even if two disk drives fail. RAID-6 requires a minimum of four disks.
RAID-10
A RAID-10 configuration combines the features of mirroring (RAID-1) and striping (RAID-0). RAID-10 is sometimes called RAID 1+0. A variation is RAID-01 or RAID 0+1 that also combines the features of mirroring and striping but implements the drives a little differently.
The minimum number of drives in a RAID-10 is four. When adding more drives, you add two (or multiples of two such as four, six, and so on). If you have four 500 GB drives used in a RAID-10, you have 1 TB of usable storage.
Q. You are a technician at a small organization. You need to add fault-tolerance capabilities within the business to increase the availability of data. However, you need to keep costs as low as possible. Which of the following is the BEST choice to meet these needs?
A. Alternate processing site
B. RAID-10
C. Backups
D. Faraday cage
Answer is B. A redundant array of inexpensive disks 10 (RAID-10) subsystem provides fault tolerance for disks and increases data availability.
An alternate processing site might be used for a mission-essential function, but it is expensive and does much more than increase the availability of data.
Backups help ensure data availability, but they do not help with fault tolerance.
A Faraday cage is a room or enclosure that prevents signals from emanating beyond the room.
See Chapter 9 of the CompTIA Security+: Get Certified Get Ahead: SY0-501 Study Guide for more information on implementing controls to protect assets.
