There are about a dozen different types of RAID that I do know of, & I will document of the more typical configurations, & usually offered on RAID controller cards.
RAID 0 is of the configurations that do not provide redundancy, making it arguably not a true RAID array. Using at least disks, RAID 0 writes knowledge to the drives in an alternating fashion, known as striping. In case you had 8 chunks of knowledge, for example, chunk 1, 3, 5 & 7 would be written to the first drive, & chunk 2, 4, 6, & 8 would be written to the second drive, but all in sequential order. This method of splitting the knowledge across drives allows for a theoretical performance boost of up to double the speed of a single hard drive, but actual world results will usually not be that lovely. Since all knowledge is not written to each disk, the failure of any drive in the array usually ends in a complete loss of knowledge. RAID 0 is lovely for individuals who require to access giant files quickly, or demand high performance across the board (i.e. betting systems). The capacity of a RAID 0 array is equal to the sum of the individual drives. So, if 160GB Seagate drives were in a RAID 0 arrays, the total capacity would be 320GB.
RAID 1 is of the most basic arrays that provides redundancy. Using at least hard drives, all knowledge is written to both drives in a method known as mirroring. Each drive's contents are identical to each other, so if drive fails, the method could continue operating on the remaining lovely drive, making it an ideal choice for those who value their knowledge. There is no performance increase as in RAID 0, & in point of fact there could be a slight decrease compared to a single drive method as the knowledge is processed & written to both drives. The capacity of a RAID array is equal to half the capacity of the sum of individual drives. Using those self-same 160GB Seagate drives from above in RAID would lead to a total capacity of 160GB.
RAID 0+1, as the name may insinuate, is a mix of RAID 0 & RAID. You have the best of both worlds, the performance boost of RAID 0 & the redundancy of RAID. A maximum of drives is necessary to implement RAID 0+1, where all knowledge is written in both a mirrored & striped fashion to the drives. Using the 8 chunks of knowledge from the example above, the write pattern would be something like this... Chunks, & 7 would be written to drives 1 & 3, & chunks 2, 4, 6, & 8 would be written to drive 2 & 4, again in a sequential manner. If drive ought to fail, the method & knowledge are still intact. The capacity of a RAID 0+1 array is equal to half the total capacity of the individual drives. So, using of the 160 GB Seagate drives ends in a total capacity of 320GB when configured in RAID 0+1.
RAID 5 may be the most powerful RAID configuration for the typical user, with (or) disks necessary. Knowledge is striped across all drives in the array, & in addition, parity knowledge is striped as well. This parity knowledge is fundamentally a check on the knowledge being written, so although all knowledge is not being written to all the drives in the array, the parity knowledge can be used to reconstruct a lost drive in case of failure. Perhaps a bit difficult to report, so let's return to the example of the 8 chunks of knowledge now being written to drives in a RAID array. Chunks & would be written to drive & respectively, with a corresponding parity chunk being written to drive. Chunks & would then be written to drives & respectively, with the corresponding parity chunk being written to drive. Chunks & would be written to drives &, with the corresponding parity chunk being written to drive. Chunks & take us back to the beginning with the knowledge being written to drives &, & the parity chunk being written to drive. It might not sound like it, but due to the parity knowledge being written to the drive not containing that specific bits of knowledge, there is full redundancy. The capacity of a RAID array is equal to the sum of the capacities of all the drives used, minus drive. So, using of the 160GB Seagate drives, the total capacity is 320GB when configured in RAID.
JBOD is another non-redundant configuration, which does not offer a true RAID array. JBOD stands for a Bunch of Disks (or Drives), & that is fundamentally all that it is. RAID controllers that support JBOD permit users to ignore the RAID functions available & fundamentally attach drives as they would to a standard drive controller. No redundancy, no performance boost, additional connections for adding more drives to a system. A smart thing that JBOD does is that it can treat the odd sized drives as in the event that they are a single volume (thus a 10GB drive & a 30GB would be seen as a single 40GB drive), so it is lovely to make use of in the event you have a bunch of odd sized drives sitting around - but otherwise it is better to go with a RAID 0, or 0+1 configuration to get the performance boost, redundancy or both.
Final Words
Implementing RAID may sound daunting to those unfamiliar with the idea, but with lots of the more basic configurations it is not much more involved than setting up a computer to make use of a standard drive controller. But, the benefits of RAID over a single drive system far outweigh the additional consideration necessary in the work of installation. Losing knowledge times due to hard drive failure may be all that is necessary to persuade somebody that RAID is right for them, but why wait until that happens.
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