Achieving fault tolerance in operating system essay

Gmail The Fault Tolerance Chronicles Fault tolerance is very desired in high-availability or life-critical systems.

Achieving fault tolerance in operating system essay

Excerpt from Term Paper: RAID provides a way to access multiple individual disks as if the array were one larger disk, spreading data access out over these multiple disks, reducing the risk of losing all data if one drive fails, and improving access time.

RAID is commonly used in large file servers, transaction of application servers, where data accessibility is critical, and fault tolerance is required.

Increasingly, RAID is also being used in desktop systems for CAD, multimedia editing and playback where higher transfer rates are needed. The capability of an array to tolerate hard disk faults depends entirely on the RAID level implemented.

There are at least ten types of RAID, presenting a myriad of feature tradeoffs that must be appropriately mapped to critical implementation requirements. Has striping but no redundancy of data. Also known as disk mirroring and consists of at least two drives that duplicate the storage of data.

There is no striping. Uses striping across disks with some disks storing error checking and correcting ECC information. Uses striping and dedicates one drive to storing parity information.

The embedded error checking information is used to detect errors. Data recovery is accomplished by calculating the exclusive OR XOR of the information recorded on the other drives.

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Uses large stripes, which means records can be read from any single drive. Includes a rotating parity array so that all read and write operations can be overlapped.

RAID-5 stores parity information but not redundant data but parity information can be used to reconstruct data. RAID-5 requires at least three and usually five disks for the array. Similar to RAID-5 but includes a second parity scheme that is distributed across different drives.

Includes a real-time embedded operating system as a controller, caching via a high-speed bus, and other characteristics of a stand-alone computer.

Offers an array of stripes in which each stripe is a RAID-1 array of drives. Offers an array of stripes in which each stripe is a RAID-3 array of disks.

However it does not offer any fault tolerance, so that if a single disk in a RAID 0 array is lost, all data is lost and will need to be recovered from backup.

Achieving fault tolerance in operating system essay

For this reason RAID 0 might be a good option for high performance workstations, but is not appropriate for mission-critical servers. This configuration produces slow writes, but relatively quick reads, and facilitates high data availability on servers because a single disk can be lost without any loss of data.

When more than two disks make up the mirror, the RAID 1 array can lose multiple disks as long as a complete mirrored pair is not lost. On the downside, the amount of physical disk space required is twice the space required to store the data. Therefore, Level 1 is most often used for applications that require very high data availability.

It was expensive and required many drives and a complex, specialized controller. The performance of RAID 2 was also low in transactional environments due to the bit-level striping. The dedicated parity disk presents a performance bottleneck when using RAID 3, especially for random writes, because it must be accessed any time anything is sent to the array Single RAID levels.

In contract, RAID 5 improves write performance by using distributed parity. RAID 3 is suitable for applications working with large files that require high transfer performance with redundancy, especially serving or editing large files and multimedia. RAID-5 volumes are well suited for reads and work well in large query or database mining applications where reads occur much more frequently than writes.

RAID 5 is also useful when a high degree of fault tolerance is required without the cost of the additional disk space needed by RAID 1. And, a RAID 5 volume is significantly more efficient than a mirrored volume when larger numbers of disks are used.

Further, the disk space that is used for parity decreases as the number of disks in the array increases.Reflections on the History of Operating Systems Research in Fault Tolerance (invited essay) ( KB) Essay accompanying the Evolution of Fault Tolerance article and talk APPEARS IN.

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Excerpt from Term Paper: Fault Tolerant Analysis of RAID Redundant Array of Independent Disks (RAID) describes array configuration and applications for multiple inexpensive hard disks, providing fault tolerance (redundancy) and improved access rates (RAID concept).

The key for achieving scalable and maintainable distributed systems is dependability, because otherwise the complexity of distribution would leave the system uncontrollable.

Hence, our approach aims at a concept for optimizing dependability. In NASA-speak: ECLSS Environmental Control And Life Support part of your spacecraft or space station that makes a livable environment so the astronauts don't all die horribly in ninety seconds flat.

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