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1. What is the difference between Mirroring and striping, provide the advantage and the disadvantage of them. (1 mark)
Striping
In a RAID 0 system data are split up in blocks that get written across all the drives in the array. By using multiple disks (at least 2) at the same time, this offers superior I/O performance. This performance can
be enhanced further by using multiple controllers, ideally one controller per disk.
Advantages
• RAID 0 offers great performance, both in read and write operations. There is no overhead caused by parity controls.
• All storage capacity is used, there is no overhead.
• The technology is easy to implement.
Disadvantages
• RAID 0 is not fault-tolerant. If one drive fails, all data in the RAID 0 array are lost. It should not be used for mission-critical systems.
Mirroring
Data are stored twice by writing them to both the data drive (or set of data drives) and a mirror drive (or set of drives) . If a drive fails, the controller uses either the data drive or the mirror drive for data recovery and continues operation. You need at least 2 drives for a RAID 1 array.
Advantages
• RAID 1 offers excellent read speed and a write-speed that is comparable to that of a single drive.
• In case a drive fails, data do not have to be rebuild, they just have to be copied to the replacement drive.
• RAID 1 is a very simple technology.
Disadvantages
• The main disadvantage is that the effective storage capacity is only half of the total drive capacity because all data get written twice.
• Software RAID 1 solutions do not always allow a hot swap of a failed drive. That means the failed drive can only be replaced after powering down the computer it is attached to. For servers that are used simultaneously by many people, this may not be acceptable. Such systems typically use hardware controllers that do support hot swapping.
2. Describe the various levels of RAID using four disks worth of data. Explain with a schema RAID 1 and RAID 2 disk configuration.
(1 mark)
levels of RAID
The most common types are RAID 0 (striping), RAID 1 and its variants (mirroring), RAID 5 (distributed parity), and RAID 6 (dual parity)
RAID 1 consists of an exact copy (or mirror) of a set of data on two or more disks; a classic RAID 1 mirrored pair contains two disks. This configuration offers no parity, striping, or spanning of disk space across multiple disks, since the data is mirrored on all disks belonging to the array, and the array can only be as big as the smallest member disk. This layout is useful when read performance or reliability is more important than write performance or the resulting data storage capacity
The array will continue to operate so long as at least one member drive is operational.
RAID 2, which is rarely used in practice, stripes data at the bit (rather than block) level, and uses a Hamming code for error correction. The disks are synchronized by the controller to spin at the same angular orientation (they reach index at the same time[clarification needed]), so it generally cannot service multiple requests simultaneously. Extremely high data transfer rates are possible
With all hard disk drives implementing internal error correction, the complexity of an external Hamming code offered little advantage over parity so RAID 2 has been rarely implemented; it is the only original level of RAID that is not currently used.