Thursday, May 09, 2002

RAID 0

RAID 0 (stripping) is the most basic form of RAID. This technology requires at least 2 disk drives to be acting in concert, with data being split between the two disks. Once a pair of drives are configured for RAID 0, they are recognized as a single, massive drive with a capacity equal to that of the two drives combined. So, if you set-up two 30GB drives for RAID 0, you end up with the equivalent of a single 60GB drive.

The magic begins when the system begins to write data to disk. Once a write occurs, the RAID controller will continue to pour data down the pipe until the drive's Write Buffer is filled. Once that has happened, rather than waiting for the buffer to be emptied (as is the case with standard IDE), the controller will redirect forthcoming data to the second drive, until its Write Buffer is filled, and so on. As a result of this set-up, the system no longer needs to standby and wait as often for data to be written to disk and write speed are effectively been doubled. And, because data has been spread-out across two separate drives, read-speed is also increased, and can also nearly be doubled.

The only problem with RAID 0 is its complete lack of data redundancy. If ever a single drive should fail, data is as good as lost because the system automatically loses half of its necessary information. RAID 0 array cannot be rebuilt and if one of the disk drives becomes corrupted or defectuous then all the data is lost forever.

RAID 1

RAID 1 (mirroring) is very different from RAID 0. Instead of spreading data out, RAID 1 involves making a copy of all data on each drive. As a result, the data you would find on one drive is exactly the same as the data you'll find on the other. Thus, if you set-up two 30GB drives for RAID 1, you end up with the equivalent of a single 30GB drive. By its very nature, this technique also effectively doubles the amount of time it takes to write data to disk. The time needed to read data, however, is cut in half, due to the fact that the same data can be read from both drives at the same time.

RAID 1 offers a very high level of data redundancy to its users as a result of its data-mirroring scheme. If either of the two drives stops functioning or becomes corrupted, no data is lost, because it can always be recovered from the remaining drive. Work can continue by either placing the remaining drive on a conventional IDE channel, or by simply swapping in a replacement for the defective part.

RAID 0+1

RAID 0+1, or RAID 10, is designed to offer the best of both worlds, but requires the presence of at least 4 hard disk drives to work. The RAID 0+1 system stripes data across one pair of drives, and then copies the results to a second pair. RAID 10 thus benefits from increased read and write speeds, as well as the extra data security of RAID 1; if one drive becomes defective, the array can still be rebuilt. The rocketRAID 404 allows a 5th drives to be designated as a Hot Spare to automatically rebuilt on the fly a broken array. The RocketRAID 404 is constatnly moniitoring the array status and in the event of a broken array caused by a bad drive, the controller will sense this situation and automatically rebuilt the array by using the designated Hot Spare drive.

Creating a RAID network.

With the RocketRAID 404, creating a RAID array is a piece of cake, whether you choose mode 0, 1, or 0+1. The first step is to simply press "CTRL + H" while the system is detecting the drives connected to the RAID controller. This will land you in the controller's BIOS, where a menu will permit you to choose which drives will be part of the array and allow you to add or remove drives, erase disks, etc...

To kick-off the creation of your very own drive array, it's sufficient to simply connect the necessary number of drives to the controller, start-up the system, drop into the controller BIOS, and select the drives you wish to use. Once that's done, restart, use Fdisk to partition the drives of the array, format the drives, and start writing data. It's that simple.

Next: Specifications.