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What Is RAID-1?
With the falling prices of hard disks these days, storage has become very cheap. Add to that the fact that media takes up more and more space. With high-definition videos, lossless music, games coming out on 2 DVDs, more and more people are going for large disks well over 500GB in size. With such large sizes comes the fact that you will be losing a lot of data if one drive goes kaput! These days, RAID solutions are very common. Even large computer manufacturers like Dell set up RAID arrays on their high-end desktop computers.
With a RAID-1 array, you need an even number of disks in the array. A RAID-1 array will basically mirror the contents of each disk to a second disk. So if you have 4 disks of 200GB each, the resulting RAID-1 array will give you 400GB of space instead of 800GB. The contents of Disk1 will be mirrored to Disk2, and the contents of Disk3 will be mirrored to Disk4. Although you lose half the capacity of the available disks, you gain reliability in the form of redundancy. If one disk fails, the mirror disk in the array will be used instead, and you will have time to install a replacement disk and synchronise the array again.
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RAID in Windows XP
Hardware RAID: you can setup a RAID array in multiple ways. The most expensive and reliable way to set it up is by buying hardware RAID cards from manufacturers like Adaptec, 3ware, and LSI Logic. These cost well into the hundreds-of-dollars amount but give lots of flexibility in the form of hot-swap support, operating-system-independent storage and very fast speeds due to their onboard drive controllers.
Windows Mirrored Volumes: if your motherboard manufacturer hasn't added RAID support in the motherboard and you'd still like to try it without breaking the bank, Windows 2000 Server will allow you to setup RAID arrays through Windows itself. While it's probably the slowest implementation of a RAID array, if you don't care about speed, it can be very useful for data redundancy. Windows XP Home/Professional versions do not support the creation of Mirrored volumes.
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Setting Up Software RAID-1 in Windows XP
Most motherboard manufacturers bundle in RAID support in their motherboards. This implementation is known as "Software RAID" or "Fake RAID" since it's basically software RAID. With this type of RAID, you have to install specific RAID drivers for each operating system you install on the computer. The storage calculations are also done by the CPU and not by a separate drive controller. This means that using the array in any way requires a lot of processor cycles. This increases the processor utilisation, is slower than hardware RAID, and creates a bottleneck in certain RAID implementations like RAID 5. Since every motherboard/chipset manufacturer implements software RAID in their own way, there are no standard instructions for setting up RAID arrays using this method.
The most common way of setting up RAID-1 in Windows XP is by utilizing your motherboard's RAID support. Certain manufacturers will bundle the RAID drivers on a floppy with the motherboard itself. Others will make you copy the drivers to an empty directory from the bundled drivers CD. The RAID-1 array has to be setup first from your computer's BIOS. Since there is no standard interface for setting up RAID arrays in BIOS with every manufacturer implementing it differently on their motherboards, you will have to rely on your motherboard's manual to set up the array first.
Once you have setup the RAID array through your computers BIOS and have the floppy with RAID drivers, boot the Windows XP installation CD. During the first loading steps, the setup will ask you to press F6 if you want to supply additional controller/storage drivers. If you've done that, it will ask you to supply a floppy with the storage/controller drivers. Proceed to the next step after loading the RAID drivers. Once it has loaded the drivers, the whole process will be as seamless as a normal install. Windows will copy the supplied drivers for use after it's installed and you can start working with your RAID-1 array.
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Software RAID, while not the fastest implementation of RAID, offers the best balance of speed and ease for free. Since almost all motherboards today come with some form of RAID implementation, it becomes very easy to check out how RAID works. To know more, check out the detailed page on Wikipedia about RAID.