Positioning and transfer performance
RAID Recovery - Positioning and transfer performance
Implementations of RAID levels vary not only on to which degree they improve read and write performance but also how they affect different kinds of read as well as write data accessibility. Data access to a single hard disk requires two tasks: getting the position of the head of the hard disk and transferring them from the hard disk platter. Therefore, the performance of hard disk depends on both positioning and transfer performance.
Multiple disks in RAID can improve positioning and transfer performance. RAID levels are categorised in part by considering the degree they improve both performance in comparison to other levels. The better improvement of positioning or transfer performance depends on users’ involvement in: reading or writing. Write can decrease the performance rate.
RAID’s basic storage techniques differ with positioning and transfer performance for read as well as write:
- Mirroring: During a read, only single drive is normally accessed but both drives can be individually accessed by the controller. This is the way how mirroring improves the positioning performance. During a write both hard disks are used but the performance is comparatively poorer than in single drive.
- Striping: It distributes information among drives in the array and every drive needs to be in a particular spot. Once the heads are all in the right place, data can be read from all the drives at the same time. It initiates improved transfer performance but doesn’t help positioning performance. While reading, smart controllers can retrieve small pieces of files from two or more parallel locations, and it advances positioning as well as transfer performance. Stripe size and width also contribute to the performance improvement.
