IBM System Storage DS3000, Programming Manual

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Table 4-5. RAID Level Configurations (continued)
RAID
Level
Configuration
6
Data protection or continuous access mode – RAID 6 stripes both user
data and redundancy data (in the form of parity) across the disk drives.
A minimum of five disk drives are required for a RAID 6 subsystem.
The equivalent capacity of two disk drives is used for the redundancy
data. Two different algorithms calculate redundancy data, which are in
the form of both a P parity and a Q parity.
RAID 6 works well for larger disk drive sizes. Recovery from a second
disk drive failure in the same subsystem is possible. If two disk drives
fail in a RAID 6 subsystem, all of the associated logical drives become
degraded, but the redundancy data permits the data to be
reconstructed. If three or more disk drives fail, all of the associated
logical drives fail, and all data is lost.
Note: RAID 6 is supported only with the following requirements:
v
Controller firmware version 7.xx.xx.xx and higher must be installed.
v
The controllers must be capable of supporting the P+Q calculation.
v
You must purchase and install a premium feature key to use RAID 6 and to use dynamic RAID-level
migration. (See “Set subsystem” on page 3-184 to set your subsystem to RAID 6.)
v
The DS4100, DS4300, DS4400, DS4500, and DS4800 storage subsystems do not support RAID 6. The
DS3500 series, DS3950, DS4200, DS4700, DS5020, DS5100, and DS5300 storage subsystems do support
RAID 6.
Hosts
A host is a computer that is attached to the storage subsystem for accessing the logical drives in the
storage subsystem. The host is attached to the storage subsystem through HBA host ports, which are
connectors on host bus adapter circuit boards. You can define specific Volume-to-LUN mappings to an
individual host or assign the host to a host group that shares access to one or more logical drives. Hosts
are identified by names or labels that users choose. The host name can be any combination of
alphanumeric characters, hyphens, and underscores. The maximum length of the host name is 30
characters.
In addition to a host name, some script commands require you to identify a host by its “type.” A host
type identifies the operating system under which the host is running (such as Windows, Solaris, or
Linux). Specifying the host type lets the controllers in the storage subsystem adapt their behavior (such as
LUN reporting and error conditions) to the operating system of the host that is sending the information.
Host types are identified by a label or an index number that is generated by the controller firmware.
Host Groups
A host group is a topological element that you can define if you want to designate a collection of hosts
that will share access to the same logical drives. A host group is a logical entity. Host groups are
identified by names or labels that users choose. The host group name can be any combination of
alphanumeric characters with a maximum length of 30 characters.
Host Bus Adapter Host Ports
A host bus adapter (HBA) provides the physical connection from the host to the storage subsystem. The
host port is a physical connector on an HBA. The HBA is a circuit board that is installed in the host. The
HBA can have one or more host ports. Each host port is identified by a unique, 16-byte World-Wide
Identifier (WWID). If the HBA has more than one host port, each host port has a unique ID.
Chapter 4. Configuring a Storage Subsystem
4-15