Since Onyx helped me with the most difficult sections in the article, I figured I may just as well post it for future reference... Thank you for your help Onyx.
BTW, this is also posted on my blog, here:
http://blog.skoups.com/?p=236
Introduction
Redundant Array of Inexpensive Disks, better known as RAID has been in existence for several years. The reasons why most people would consider using RAID is that they need faster data transfer speed from the drives, require redundancy, need a bigger single drive, or, in most instances, a combination of these reasons.
The first section of this document will deal with explaining what factors impact the speed of mechanical hard drives. At the end of the section, you should know what to look for when purchasing a new hard drive and what to avoid. The second section will cover the popular RAID formats as well as discussing the pros and cons of each. The final section covers nested RAID.
Rotational based hard drives
Before we start delving into RAID and more specifically the read/write speed, it is imperative that we review the inner workings of spinning (or mechanical) hard drives. The basic mechanical concept of the magnetic hard drive has not changed for several decades. The concept still relies on a spinning platter that can hold a magnetic charge, with a magnetic head to read and write bits (0 or 1) to and from the platter. By changing the number of platters, the hard drive manufacturers could tailor their products for more energy conservation or more performance. A typical hard drive usually contains several platters.
The first drives weighed several tons and produced only a couple of megabytes. Today, the biggest single drive amounts to 3TB (or 3,000,000,000,000 bytes). The actual space available on a 3TB drive however only amounts to 2.7TiB in the operating system. This difference boils down to the way the hard drive manufactures use 1000s to differentiate between kilo, mega, giga and terra whereas standard operating systems use 1024 between each jump. The correct way to differentiate between the two formats is to use the terms terabyte (TB) and tebibyte (TiB). The latter term refers to the binary number typically associated with the space available in the operating system. In other words, the drive is actually a 3TB drive but it only has 2.7TiB space in the operating system.
Key things that differentiate hard drives, apart from the size, are the following:
1. Rotation speed
2. Speed variations on the same drive (read/write speed at the beginning and end of the drive)
3. Consecutive read / write speed
4. Random read / write speed
5. Seek time
Rotation Speed
The rotation speed indicates the speed at which the platters spin. A typical laptop drive spins at 5400RPM, while a SATA drive spins at 7200RPM. SAS / SCSI and
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