Number 281 - October 2006

Should Your System Be RAIDed
by Vinny La Bash, vlabash@comcast.net, Sarasota Personal Computer Users Group, Inc.
You may have heard fellow computer enthusiasts brag about their new fast RAID system as if it were a high performance sports car. If you wondered what they were talking about, you are not alone.    Just what does RAID stand for? The source of the RAID acronym can be credited to three University of California Berkeley professors named Patterson, Gibson, and Katz. In 1987 they published a paper named "A Case for Redundant Arrays of Inexpensive Disks (RAID)". The fundamental concept of RAID was to combine multiple small disks into an arrangement yielding greater performance than a Single Large Expensive Drive (SLED). If you can see the potential to combine the acronyms to make bad jokes, again you are not alone.    The main objection to RAID was that two or more disk drives are inherently less reliable than a single disk drive. The professors overcame the objection by showing that disk arrays can be made more reliable by storing data redundantly in various ways across multiple disk drives.    The paper defined five types of RAID arrangements, each offering different trade-offs in features and performance. Over time, more RAID configurations were added to the mix. The corporate world gradually adopted RAID, but it never took the PC world by storm because until relatively recently, disk drives were not "inexpensive".    At the core of RAID is a process called "striping". With several hard drives connected to a controller card installed in a motherboard slot, you can juice up read and write speeds by breaking the data into blocks (stripes) and storing these blocks across multiple disk drives. This allows data to be either recorded or accessed in multiple blocks simultaneously across multiple drives in parallel. Without going into technical detail, the parallel operation provides the increase in performance. Of the many RAID configurations developed since 1987 only two are likely to be incorporated into a PC, and one of those isn't really RAID at all because it has no redundancy. The other is true RAID, but does not use striping.    We'll start out with RAID 1, also known as Disk Mirroring. The title gives it away. In a two disk array you mirror the contents of one disk onto the other. With 100% redundancy, there is no need to do any kind of data restoration if one of the disks should fail for any reason. A few simple instructions allow you to use the mirrored disk until you can install a replacement for the failed drive. Reactivate your array, and you're back in business with no down time. The trade-off is that a second disk doesn't give you any additional disk space, nor does it appreciably affect performance one way or the other. If reliability and preservation of data are all important to you, then a RAID 1 array can make good sense. RAID 1 is relatively cheap, easy to use, and costs about the same as most conventional backup solutions. Turn to RAID 1 when data integrity is	more important than performance. To set up a RAID for your internal drives, you will need support on your motherboard or add-in card. Finally, you must still keep current drive backups to protect against user errors, viruses, and other problems that affect both drives.    Hard core gamers and other performance obsessed nut cases are almost always referring to RAID 0 when they brag about their PC speed demons. Most of them either don't know or care that RAID 0 is not true RAID as it has no redundancy. Data is spread out among all the drives in the array, which means that if any one of your drives fail, all your data is lost. This is not important if you use your system solely for game playing, but how many of us do that? If you have important data stored on your system, RAID 0 can be a dangerous implementation that may ultimately trash every byte of information on your system.    A better way than RAID 0 is to install a hard drive with a disk cache of at least 8 Megabytes of RAM. Because computers can access data from RAM much faster than directly from a disk, caching can significantly increase performance though it won't match RAID 0. Many cache systems also attempt to predict what data will be requested next so they can place that data in the cache ahead of time. This will never stop performance crazy freaks from using RAID 0. They all backup their systems regularly, don't they?    RAID 0 is for those enamored of performance where loss of data is of little concern. As an alternative, you can approach RAID 0 performance by installing drives with at least 8 megabytes of disk cache.    While it does not obviate the need for backup, a RAID 1 array can provide additional protection for those whose main consideration is preservation of data.    There are many different types of RAID configurations which we have not discussed. We have confined our dialog to RAID 0 and 1 because they are the most common arrangements on home computers. Most technical details have been left out for simplification.    For a complete description of RAID, including animated diagrams of how data is actually stored, go to    Copyright 2006. This article is from the September 2006 issue of the Sarasota PC Monitor, the official monthly publication of the Sarasota Personal Computer Users Group, Inc., P.O. Box 15889, Sarasota, FL 34277-1889. Permission to reprint is granted only to other non-profit computer user groups, provided proper credit is given to the author and our publication.
Number 281 - October 2006