raid - not just for bugs

Information about raid - not just for bugs

Published on June 5, 2011

Author: Marcine

Source: authorstream.com

Content

RAID: RAID Not Just For Bugs! By Marcine E. Lohman RAID: RAID RAID is a technology that is used to increase the performance and/or reliability of data storage. The abbreviation stands for Redundant Array of Independent Disks . RAID is now used as an umbrella term for computer data storage schemes that can divide and replicate data among multiple physical disk drives. T here is a trend to also use the technology for solid state drives . RAID Software: RAID Software The software to perform the RAID-functionality and control the hard disks can either be located on a separate controller card (a hardware RAID controller) or it can simply be a driver. Some server systems, such as Windows Server 2003 or Mac OS X include software RAID functionality. Hardware RAID controllers cost more than pure software but they also offer better performance. RAID Systems: RAID Systems RAID-systems can be based with an number of interfaces, including SCSI, IDE, SATA or FC ( fiber channel.) There are systems that use SATA disks internally but that have a FireWire or SCSI-interface for the host system . RAID Levels: RAID Levels There are different RAID levels, each suiting specific situations. RAID levels are not standardized by an industry group. This explains why companies are sometimes creative and come up with their own unique implementations . RAID Disks: RAID Disks Sometimes disks in a RAID system are defined as JBOD, which stands for ‘Just a Bunch Of Disks’ . This means that those disks do not use a specific RAID level and are used as if they were stand-alone disks. This is often done for disks that contain swap files or spooling data . RAID 0: Striping: RAID 0: Striping In a RAID 0 system, data is split up into blocks that get written across all the drives in the array. By using multiple disks (at least 2) at the same time, RAID 0 offers superior I/O performance. This performance can be enhanced further by using multiple controllers, ideally one controller per disk. RAID 0: Striping: RAID 0: Striping RAID 0 Advantages: RAID 0 Advantages RAID 0 offers great performance, both in read and write operations. There is no overhead caused by parity controls. All storage capacity can be used, there is no disk overhead. The technology is easy to implement . RAID 1: Mirroring: RAID 1: Mirroring Data is stored twice by writing to both the data disk (or set of data disks) and a mirror disk (or set of disks ). If a disk fails, the controller uses either the data drive or the mirror drive for data recovery and continues operation. You need at least 2 disks for a RAID 1 array. RAID 1: Mirroring: RAID 1: Mirroring RAID 1 Advantages: RAID 1 Advantages RAID 1 offers excellent read speed and a write-speed that is comparable to that of a single disk. In case a disk fails, data does not have to be rebuilt, it just has to be copied to the replacement disk. RAID 1 is a very simple technology . RAID 3: RAID 3 On RAID 3 systems, datablocks are subdivided (striped) and written in parallel on two or more drives. An additional drive stores parity information. You need at least 3 disks for a RAID 3 array . RAID 3: Parity on Separate Disk: RAID 3: Parity on Separate Disk RAID 3 Advantages: RAID 3 Advantages RAID-3 provides high throughput (both read and write) for large data transfers. Disk failures do not significantly slow down throughput . RAID 5: RAID 5 RAID 5 is the most common secure RAID level. Instead of a dedicated parity disk, parity information is spread across all the drives. You need at least 3 disks for a RAID 5 array. RAID 5: Parity Across Disks: RAID 5: Parity Across Disks RAID 5 Advantages: RAID 5 Advantages Read data transactions are very fast while write data transaction are somewhat slower (due to the parity that has to be calculated ). The End: The End

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