Active/Active disk arrays

This type of multipathed disk array lets you access a disk in the disk array through all the paths to the disk simultaneously, without any performance degradation.

Active/Passive disk arrays

This type of multipathed disk array allows one path to a disk to be designated as primary and used to access the disk at any time. Using a path other than the designated active path results in severe performance degradation in some disk arrays.

ALUA

Asymmetric Logical Unit Access. A protocol specified in the SCSI-3 standard that is used by Asymmetric Active/Active (A/A-A) arrays.

block

The minimum unit of data transfer to or from a disk or array.

cluster

A set of hosts (each termed a node) that share a set of disks.

device name

The device name or address used to access a physical disk, such as hdisk3, which indicates the whole of disk 3.

The device name or address used to access a physical disk, such as c0t0d0. The c#t#d# syntax identifies the controller, target address, and disk.

The device name or address used to access a physical disk, such as sda or sda3, where sda indicates the whole device, and sda3 refers to the third partition on sda.

The device name or address used to access a physical disk, such as c0t0d0s2. The c#t#d#s# syntax identifies the controller, target address, disk, and slice (or partition).

In a SAN environment, it is more convenient to use enclosure-based naming, which forms the device name by concatenating the name of the enclosure (such as enc0) with the disk's number within the enclosure, separated by an underscore (for example, enc0_2). The term disk access name can also be used to refer to a device name.

disabled path

A path to a disk that is not available for I/O. A path can be disabled due to real hardware failures or if the user has used the vxdmpadm disable command on that controller.

disk

A collection of read/write data blocks that are indexed and can be accessed fairly quickly. Each disk has a universally unique identifier.

disk access name

An alternative term for a device name.

disk array

A collection of disks logically arranged into an object. Arrays tend to provide benefits such as redundancy or improved performance.

disk array serial number

This is the serial number of the disk array. It is usually printed on the disk array cabinet or can be obtained by issuing a vendor- specific SCSI command to the disks on the disk array. This number is used by the DMP subsystem to uniquely identify a disk array.

disk controller

In the multi-pathing subsystem, the controller (host bus adapter or HBA) or disk array connected to the host.

disk enclosure

An intelligent disk array that usually has a backplane with a built-in Fibre Channel loop, and which permits hot-swapping of disks.

disk ID

A universally unique identifier that is given to each disk and can be used to identify the disk, even if it is moved.

disk media name

An alternative term for a disk name.

disk name

A logical or administrative name chosen for a disk that is under the control of DMP DSM, such as disk03. The term disk media name is also used to refer to a disk name.

DMP DSMs

Dynamic Multi-Pathing device-specific modules. DMP DSMs are designed to support a multipath disk storage environment setup with the Microsoft Multipath I/O (Microsoft MPIO) solution. DMP DSMs work effectively with Windows to provide a fault tolerant multipath disk storage environment. DMP DSMs provide Windows Storport driver support.

DMP

A short name for the product Dynamic Multi-Pathing.

enabled path

A path to a disk that is available for I/O.

enclosure

See disk enclosure.

enclosure-based naming

See device name.

failover

An automatic process where an alternative path to data on a storage array is activated when the current data path fails.

fault tolerance

The characteristic of ensuring data integrity and system functionality when hardware failures occur.

Fibre Channel

A collective name for the fiber optic technology that is commonly used to set up a storage area network (SAN).

JBOD (just a bunch of disks)

The common name for an unintelligent disk array which may, or may not, support the hot-swapping of disks.

load balancing

The process of balancing the data load between disks so that I/O demands are spread as evenly as possible across an I/O subsystem's resources. With DMP, load balancing is achieved either by moving subdisks between disks or by using the Active/Active path configuration with DMP to distribute the data load across multiple disks.

LUN

Logical unit number . The number that, when combined with the Target ID, uniquely identifies a disk on the port.

MPIO

Microsoft Multipath I/O. A Windows-based multi-pathing framework that interacts with DMP DSMs.

multi-pathing

Where there are multiple physical access paths to a disk connected to a system, the disk is called multi-pathed. Any software residing on the host, (for example, the DMP driver) that hides this fact from the user is said to provide multi-pathing functionality.

node

One of the hosts in a cluster.

path

When a disk is connected to a host, the path to the disk consists of the HBA (host bus adapter ) on the host, the SCSI or fibre cable connector and the controller on the disk or disk array. These components constitute a path to a disk. A failure on any of these results in DMP trying to shift all I/O for that disk onto the remaining (alternate) paths.

primary path

In Active/Passive disk arrays, a disk can be bound to one particular controller on the disk array or owned by a controller. The disk can then be accessed using the path through this particular controller.

RAID (redundant array of independent disks)

A disk array set up with part of the combined storage capacity used for storing duplicate information about the data stored in that array. This makes it possible to regenerate the data if a disk failure occurs.

secondary path

In Active/Passive disk arrays, the paths to a disk other than the primary path are called secondary paths. A disk is supposed to be accessed only through the primary path until it fails, after which ownership of the disk is transferred to one of the secondary paths.

SAN (storage area network)

A networking paradigm that provides easily reconfigurable connectivity between any subset of computers, disk storage and interconnecting hardware such as switches, hubs and bridges.

target ID

The number that, when combined with the LUN, uniquely identifies a disk on the port.