NT1230
1/1/16
Unit 2 Assignment 1 Disk Redundancy Research
RAID stands for redundant array of independent disks and is a data storage virtualization technology that combines multiple physical drives into a single logical unit for the purpose of backing up vital data, improving system performance, or both. It’s most useful for businesses because they usually network terminals that all pull from a central server with everything stored on it. RAID is used to allow for a seamless replacement of defective drives or swapping full drives for empty ones without hassle of having to reboot.
There are four types of raid that are going to be discussed and there is also a difference between hardware RAID and software RAID. Software RAID is just software that runs on your operating system, hardware RAID uses a modified chip as a controller and assists the software for operating systems that software RAID is incompatible with.
RAID 0 consists of striping, without mirroring or parity. The capacity of a RAID 0 volume is the sum of the capacities of the disks in the set, the same as with a spanned volume. There is no added redundancy for handling disk failures, just as with a spanned volume. Thus, failure of one disk causes the loss of the entire volume, with reduced possibilities of data recovery when compared to a broken spanned volume. Striping distributes the contents of files roughly equally among all disks in the set, which makes concurrent read or write operations on the multiple disks almost inevitable and results in performance improvements. The concurrent operations make the throughput of most read and write operations equal to the throughput of one disk multiplied by the number of disks. Increased throughput is the big benefit of RAID 0 versus spanned volume.
RAID 1 also consists of data mirroring, without parity or striping. Data is written identically to two or more drives, thereby producing a "mirrored set" of drives. Thus, any read request can be serviced by any drive in the set. If a request is broadcast to every drive in the set, it can be serviced by the drive that accesses the data first improving performance. Sustained read throughput, if the controller or software is optimized for it, approaches the sum of throughputs of every drive in the set, just as for RAID 0. Actual read throughput of most RAID 1 implementations is slower than the fastest drive. Write throughput is always slower because every drive must be updated, and the slowest drive limits the write performance. The array continues to operate as long as at least one drive is functioning. It’s the most expensive but the most straightforward in implementation which is what businesses who don’t understand the complex details and don’t have the time to learn that opt for this instead of saving money.
RAID 5 consists of block-level striping with distributed parity. Unlike RAID 4, parity information is distributed among the drives, requiring all drives but one to be present to operate. Upon failure of a single drive, subsequent reads can be calculated from the distributed parity such that no data is lost. RAID 5 requires at least three disks. RAID 5 is seriously affected by the general trends regarding array rebuild time and the chance of drive failure during rebuild. Rebuilding an array requires reading all data from all disks, opening a chance for a second drive failure and the loss of the entire array.
RAID 6 consists of block-level striping with double distributed parity. Double parity provides fault tolerance up to two failed drives. This makes larger RAID groups more practical, especially for high-availability systems, as large-capacity drives take longer to restore. RAID 6 requires a minimum of four disks. As with RAID 5, a single drive failure results in reduced performance of the entire array until the failed drive has been replace. With a RAID 6 array, using drives from multiple sources and manufacturers, it is possible to mitigate most of the problems associated with RAID 5.
For my purposes I would probably just get RAID 1 because it allows for identical backups and that’s all I need.
References
RAID. (2015, December 3). Retrieved 2016, from https://en.wikipedia.org/wiki/RAID