The first thing we'd recommend is backing up all of your data. Ensure that all of the data on your existing drives is backed up and that you've taken a fresh image of your OS installation. (This guide has nitty-gritty details on how to do just that.) If something goes wrong and you lose data, you'll be happy to have a backup in place. And if setting up RAID somehow mangles your OS, having a fresh image on hand will help you recover in no time.
Note, however, that if you plan to migrate an existing OS installation that resides on a single drive to a new RAID volume, the configuration changes necessary to set up RAID may cause problems with the OS and render it non-bootable. It's best to install a fresh OS onto a new RAID array whenever possible.
RAID hardware considerations
The vast majority of motherboards sold today have built-in support for RAID. The drive controllers integrated into Intel's and AMD's chipsets offer RAID (as do most other lesser-known chipsets) and many motherboard manufacturers often integrate additional RAID controllers, from companies like Marvell, onto their boards as well. It's common for on-board RAID controllers to support RAID 0, 1, 5, and JBOD, though some also support RAID 10. Keep in mind though, that even on the off chance your motherboard doesn't have built-in RAID support, software RAID is still most likely possibly, provided the board has a couple of open SATA ports to connect additional drives.
Though the RAID controllers integrated into most motherboards should be adequate for the vast majority of users, higher-end add-in solutions are also available. Typically, inexpensive add-in boards (think under $150) feature the same basic standalone controllers found on many motherboards, but some higher-end offerings like those from Areca, LSI, or 3COM offer true hardware RAID, with dedicated storage processors and cache memory.
Setting up hardware RAID
Configuring an array with a hardware RAID controller is fairly straightforward. If you're using an add-in board, the first step is to actually install the card. Power down your system, insert that card into an available PCI-E slot, power up the system, and install whatever drivers are necessary for your OS. Installing a RAID controller card is really no different than any other add-in board.
If you're planning to use your motherboard's on-board RAID controller, the first step is to enter your system BIOS/UEFI, navigate to the integrated peripherals or SATA menu, and enable RAID, since most of today's motherboard default to legacy IDE or AHCI modes.
Once RAID support is enabled (or your add-in card is installed), the next step is to physically connect your storage drives. Mount the drives into any available bays in your system, connect their power and data cables, and that's basically it. When you boot your system with RAID enabled, you'll see a prompt to enter the RAID controller's option ROM, usually by pressing CTRL + I or CTRL + S.
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