Disk array overview

Disk arrays are groups of disks that work together with a specialized array controller to potentially achieve higher data transfer and input and output (I/O) rates than those provided by single large disks. The array controller keeps track of how the data is distributed across the disks. RAID 5, 6, and 10 disk arrays also provide data redundancy so that no data is lost if a single disk in the array fails.

Note: This topic and the iprconfig utility use common terminology for disk formats:

JBOD
A JBOD disk is formatted to 512 bytes/sector. JBOD stands for "Just a Bunch Of Disks". A JBOD disk is assigned a /dev/sdX name and can be used by the Linux® operating system.
Advanced function
An advanced function disk is formatted to 528 bytes/sector. This format allows disks to be used in disk arrays. An advanced function disk cannot be used by the Linux operating system directly. The Linux operating system can use an advanced function disk only if it is configured into a disk array.

Disk arrays are accessed in Linux as standard SCSI disk devices. These devices are automatically created when a disk array is created, and deleted whenever a disk array is deleted. The individual physical disks that comprise disk arrays (or are candidates to be used in disk arrays), which are formatted for advanced function, are hidden from Linux and are accessible only through the iprconfig utility. Linux sees all JBOD disks. These disks must be formatted for advanced function before they can be used in disk arrays. For information on formatting JBOD disks to make them available for use in disk arrays, see Formatting to JBOD.

An advanced function disk can be used in one of three roles:

Array Member: An advanced function disk which is configured as a member of a disk array.
Hot Spare: An advanced function disk assigned to a controller waiting to be used by the controller to automatically replace a Failed disk in a Degraded disk array.
Array Candidate: An advanced function disk which has not been configured as a member of a disk array or a hot spare.

The Display Hardware Status option in the iprconfig utility can be used to display these disks and their associated resource names. For details regarding how to view the disk information, see Viewing device status. The following sample output is displayed when the Display Hardware Status option is invoked:

+--------------------------------------------------------------------------------+
|                             Display Hardware Status                            |
|                                                                                |
|Type option, press Enter.                                                       |
|  1=Display hardware resource information details                               |
|                                                                                |
|OPT Name   PCI/SCSI Location          Description               Status          |
|--- ------ -------------------------- ------------------------- ----------------|
|           0000:00:01.0/0:            PCI-X SAS RAID Adapter    Operational     |
|    sda    0000:00:01.0/0:4:2:0       Physical Disk             Active          |
|    sdb    0000:00:01.0/0:4:5:0       Physical Disk             Active          |
|           0000:00:01.0/0:4:10:0      Enclosure                 Active          |
|           0000:00:01.0/0:6:10:0      Enclosure                 Active          |
|           0000:00:01.0/0:8:0:0       Enclosure                 Active          |
|           0002:00:01.0/1:            PCI-X SAS RAID Adapter    Operational     |
|    sdc    0002:00:01.0/1:0:1:0       Physical Disk             Active          |
|    sdd    0002:00:01.0/1:0:2:0       Physical Disk             Active          |
|           0002:00:01.0/1:0:4:0       Advanced Function Disk    Active          |
|           0002:00:01.0/1:0:5:0       Advanced Function Disk    Active          |
|           0002:00:01.0/1:0:6:0       Advanced Function Disk    Active          |
|           0002:00:01.0/1:0:7:0       Hot Spare                 Active          |
|    sde    0002:00:01.0/1:255:0:0     RAID 0 Disk Array         Active          |
|           0002:00:01.0/1:0:0:0         RAID 0 Array Member     Active          |
|    sdf    0002:00:01.0/1:255:1:0     RAID 6 Disk Array         Active          |
|           0002:00:01.0/1:0:10:0        RAID 6 Array Member     Active          |
|           0002:00:01.0/1:0:11:0        RAID 6 Array Member     Active          |
|           0002:00:01.0/1:0:8:0         RAID 6 Array Member     Active          |
|           0002:00:01.0/1:0:9:0         RAID 6 Array Member     Active          |
|           0002:00:01.0/1:0:24:0      Enclosure                 Active          |
|           0002:00:01.0/1:2:24:0      Enclosure                 Active          |
|                                                                                |
|                                                                                |
|                                                                                |
|                                                                                |
|                                                                                |
|e=Exit   q=Cancel   r=Refresh   t=Toggle                                        |
+--------------------------------------------------------------------------------+

Disk array, physical disk, and I/O adapter (IOA) states are displayed in the fifth column of the Display Hardware Status screen.