Glossary

 

Array

As used in RAID, an array consists of one or more hard drives which are logically combined to form a single storage drive. Arrays are categorized by the method in which they are accessed to logically organize data on them for purposes of performance enhancement, capacity augmentation, and /or data redundancy protection. The different types of arrays include RAID 0 (Striping), RAID 1 (Mirroring), RAID 0/1 (Mirrored Striping), RAID 1/0 (Striped Mirroring), RAID 5, etc.

Controller

A system may include RAID Controllers. They provide RAID 0, RAID 1, RAID 0/1, JBOD, Spare and Hot Swap functions. There are two channels on each controller. One is channel 0 (Primary Channel) and the other is channel 1 (Secondary Channel).

Channel

A bus that uses some protocol to move data to/ from the disks. The channel provides a connection between controller and devices (Array or physical disk). Each channel can attach a master device and a slave device.

Hot Swap

To pull out a component from a system and plug in a new one while the power is still on and the unit is still operating. Note: Ensure that your system supports hot swappable drives before executing this operation.

JBOD (Volume)

JBOD is an acronym for Just a Bunch of Disks. It is used to refer to hard disks that are not 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 one single physical disk (not member of an array and not an ATAPI device or a removable disk), you can create a JBOD array.

Mirroring

It refers to a data protection technique that duplicates data from one drive to another. This is known as RAID Level 1.

RAID

Redundant Array of Independent Disks (RAID) refers to a method of organizing data on one or more physical disks to provide increased I/O performance and data protection. The different methods for organizing the data are referred to as RAID Levels.

RAID 0 (Striping)

RAID 0 is typically defined as a group of striped disk drives without parity or data redundancy. RAID 0 arrays can be configured with large stripes for multi-user environments or small stripes for single-user systems that access long sequential records. 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.  

RAID 1 (Mirroring)

Also known as mirroring. Mirroring refers to the 100% duplication of data from one disk to another.  Due to 100% duplication, this is a costly solution.

 

RAID 0/1 (Mirrored Striping)

A combination of RAID 1 and RAID 0. RAID 0/1 can provide much more speed and security. Only when four single physical disks are available, you can create a RAID 0/1 array.

Stripe

A stripe is interleaved data across multiple drives in an array. Data is sequentially stored in allocated sizes across disks, based on the RAID level. Stripe size is the number of drives x the strip size.

Stripe Size

Stripe size is the size of the logically contiguous data block recorded on all drives connected to the controller. A variable stripe size allows for the configuration of the stripe size. The stripe size for a volume can be configured to one of several sizes (16k, 32k or 64k).

 

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