Glossary
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A computer with HighPoint RAID Controller, driver for the controller, and HighPoint Storage Management Service installed. Users can use HighPoint Storage Management Console to connect it and manage the RAID system. A system may include one or more RAID controllers. A controller provides hardware control to devices. There are several channels on each controller. A channel provides the connection between controller and device (array or physical disk). Each channel can attach a master device and a slave device. A device attached to the adapter. It can be an IDE hard drive or an ATAPI device such as CD-ROM or Tape. The detection of a disk failure will result in an event being recorded in the Event Log, which will trigger a critical warning message. A spare disk can be used as a replacement by a redundant array when a failure occurs. A logical container which includes several spare disks. When needed, the spare disks can be picked up sequentially. A spare disk that can only be used for a specified array. Initializing completely obliterates any information previously stored on the selected disks. RAID is an acronym for Redundant Array of Inexpensive (or Independent) Disks. A RAID array is a collection of drives which collectively act as a single storage system, which can tolerate the failure of a drive without losing data, and which can operate independently of each other. The benefits of RAID can include: higher data transfer rates for increased server performance, increased overall storage capacity for a single drive designation (i.e. C, D, E, etc.), data redundancy/fault tolerance for ensuring continuous system operation in the event of a hard drive failure. Different types of arrays use different organizational models and have varying benefits. The following outline breaks down the properties for each type of RAID array. When a disk array is striped, the read and write blocks of data are interleaved between the sectors of multiple drives. Performance is increased, since the workload is balanced between drives (or ¡°members¡±) that form the array. Identical drives are recommended for performance as well as data storage efficiency. The disk array¡¯s data capacity is equal to the number of drive members multiplied by the smallest array member¡¯s capacity. For example, one 1 GB and three 1.2GB drives will form a 4GB (4*1GB) disk array instead of 4.6 GB. The stripe block size value can be set logically from 1KB, 2KB, 4KB, 8KB, 16KB, 32KB, 64KB [Default], 128KB, 256KB, 512KB, or 1024KB. This selection will directly affect performance. Larger block sizes are better for random disk access (like email, POS, or web servers), while smaller sizes are better for sequential access. RAID 0 arrays deliver the best data storage efficiency and performance of any array type. The disadvantage is that if one drive in a RAID 0 array fails, the entire array fails. When a disk array is mirrored, identical data is written to a pair of drives, while reads are performed in parallel. The reads are performed using elevator seek and load balancing techniques where the workload is distributed in the most efficient manner. Whichever drive is not busy and is positioned closer to the data will be accessed first. Under RAID 1, if one physical drive suffers a mechanical failure or sector error, the other mirrored drive continues to function. This is called Fault Tolerance. Moreover, if a spare drive is present, the spare drive will be used as the replacement drive and data will begin to be mirrored to it from the remaining good drive. Due to the data redundancy of mirroring, the drive capacity of the array is only the size of the smallest drive. For example, two 1 GB drives which have a combined capacity of 2GB instead would have 1GB of usable storage when set up in a mirrored array. Similar to RAID 0 striping, if drives of different capacities are used, there will also be unused capacity on the larger drive. RAID 1 delivers the best performance of any redundant array type. RAID 5 (Stripe with Rotating Parity) This type of array is composed of independent data disk with distributed parity blocks. Each entire data block is written on a data disk; parity for blocks in the same rank is generated on Writes, recorded in a distributed location and checked on Reads. RAID 5 requires a minimum of 3 drives to implement. This type of RAID owns the highest Read data transaction rate. Mirrored Striping combines both of the previous array types. It can increase performance by reading and writing data in parallel while protecting data with duplication. A minimum of four drives is needed for Mirrored Striping to be installed. With a four-drive disk array, two drives are striped together, and a second pair of striped drives is used to mirror the first pair of striped drives. The data capacity is similar to a standard mirroring array, with half of the total storage capacity dedicated for redundancy. An added plus for using RAID 0/1 is that, in many situations, such an array offers double fault tolerance. Double fault tolerance may allow your data array to continue to operate depending on which two drives fail. RAID 1/0 is implemented as a striped array whose segments are RAID 1 arrays. It has the same fault tolerance as RAID 1 and the same overhead for fault-tolerance as mirroring alone. It owns the very high reliability combined with high performance. The technique of combining a set of disk partitions located on different hard disks into a single volume, creating a virtual ¡°stripe¡± across the partitions that the operating system recognizes as a single drive. Disk striping can occur at the bit level or at the sector level and allows multiple concurrent disk accesses that can improve performance considerably. A fault-tolerant technique that writes the same information simultaneously onto two hard disks or two hard-disk partitions, using the same disk controller. If one disk or partition fails, information from the other can be used to continue operations. It is offered by most major network operating systems. It is also known as RAID 1. JBOD is an acronym for Just a Bunch of Disks. It is used to refer to hard disks that aren't configured according to RAID -- a subsystem of disk drives that improves performance and fault tolerance. JBOD provides much more capacity (the sum of all the disks). If there is more than a single physical disk (not member of an array and not an ATAPI device or a removable disk), you can create a JBOD array. |