Redundant array of independent disks features - Term Paper Example

Download file to see previous pages The disks used in array are independent of each other thus reducing the cost of implementing the arrays. (Dawkins and Arnold 2006). Architecture: The following are some of commonly used RAID levels: RAID 0: it is the level without parity or zero redundancy. It has a minimum number of two drives and provides improved performance and additional storage but has no fault tolerance and thus the simple stripe sets are referred to as RAID 0. RAID 0 does not implement error checking mechanism and hence any error is uncorrectable (Hennessy and Patterson, 2009). When more disks are used in the array it implies that it has higher bandwidth, but greater risk of losing data. RAID 1: This is the level of mirroring without parity or striping, here data is written identically to multiple disks. Many implementations create sets of two disks but some sets may contain three or more disks. The array provides fault tolerance from disk failures and it functions when at least one of drives is functioning. It has the key weakness which is high cost overhead; this is because data is duplicated as required by storage capacity. RAID 2: it is the level with bit striping that has dedicated Hamming-code parity, in this level there is a synchronized rotation of disks and data is striped such that each sequential bit is on it is own disk (Hennessy and Patterson, 2009). When Hamming-code parity is calculated across the subsequent bits on disks it is then stored on the parity disks available. RAID 3: it is a byte-level striping that has dedicated parity, disks spindle rotate in a synchronized manner and data is striped in such a way that all the subsequent bytes are stored on different disks. Dedicated parity disk is used to store the parity after it has been calculated across the corresponding bytes on disks. RAID 4: it a striping block level that has dedicated parity, in this architecture all parity data is confined to a single disk which can lower its performance. In this arrangement, there is a spread of files between many disks. The disks in this array have independent operations allowing I/O requests to be done in a similar way, though the drawback is that data transfer speeds suffer as a result of the type of parity being used. RAID 5: it is a level of block striping whose parity is distributed. Data is distributed along with the parity and drives are required to be present in order for it to operate implying that if a fails occurs then it will have to be replaced, however, an array is not destroyed when a single drive fails. When the drive fails, any next reads is calculated from the distributed parity such that when drive fails then it is protected from the end user (Hennessy and Patterson, 2009). Design Issues: The booting process is the key concern in the RAID based operating systems. At times it can be difficult to come up with a boot process that can fail to another drive if the normal boot process fails. When the system fails then a manual intervention has to use so as to make the system become bootable after another failure. A hardware RAID controller has an explicit programming which identifies the broken disk. Hardware RAID controllers at times has battery that is covered by cache memory. In the modern system, for data to be safe then the user of software RAID has to ensure that the write-back cache on the disk is off. When the write cache is turned off, it has a performance penalty accompanied with it which relies on the amount of workload and the command queuing in the disk system. The use of RAID controller that has battery backed ...Download file to see next pagesRead More