APC RAID Subsystem SCSI-SATA II Informações Técnicas descarregar pdf (Página 129)

Advanced Functions

5-11

Configuration Tasks

5.3 Redundant Controller

5.3.1 Overview

Redundant controller is a high-availability solution for ensuring system availability against controller failure and for

improving the performance by doubling the I/O processing power. A redundant-controller system incorporates two active-

active controllers that can service I/O concurrently and take over each other if any controller fails. This section introduces

basic concept of redundant-controller operations.

• Dual controller configuration and status synchronization

The two controllers synchronize with each other by the dedicated high-speed Redundant-controller Communication

Channels (RCC) on the system backplane. The synchronization allows a controller to know the configurations and status

of the peer controller, such that it can take over the jobs of a failed peer controller. It also allows you to access any one

controller to monitor the status of the system or to do configurations for both controllers.

• Mirrored write cache

A controller caches data in the memory for performance when the delay-write option is turned on. To ensure that the

cached data can be retained, data written to one controller is also forwarded to the peer controller. The RCC also serves

as the path of data forwarding for mirroring write cache. You may also disable the write cache mirroring by the UI (see

Mirrored Write Cache Control option on Section 2.7.15).

• Controller failover and failback

Both controllers monitor each other by periodic heartbeat signaling packets exchanged over the RCC. If a controller

detects that the RCC link is offline or the heartbeat signal is not received within a period of time, it will power off the peer

controller and start the controller failover procedure. The I/O access to the faulty controller will be redirected to the

surviving controller, and the background tasks will also be continued by the surviving controller.

When the faulty controller is replaced by a new controller, the surviving controller will negotiate with the replacement

controller to perform the controller failback procedure. The replacement controller will get synchronized with the surviving

controller to learn the latest status and configurations. After that, the surviving controller will stop servicing the I/O for the

peer controller, and the replacement controller will take back all the background tasks.

• Multi-path IO (MPIO) and controller preference

When using SAS host interface or using FC host interface without a switch, the redundant-controller system requires

MPIO driver installed at host side for I/O redirection during controller failover and failback. You have to symmetrically

export the same LUN mappings for all host-interface ports, such that a virtual disk can be seen by all I/O paths of both

controllers and controller failover/failback can work. After LUN configurations and host-interface connections are done,

please install the MPIO drivers provided by your RAID system supplier to set up the redundant-controller configurations.

The redundant-controller solution is compliant with T10 TPGS (Target Port Group Standard) architecture. When a virtual

disk is created, one of the two controllers is assigned to it as the preferred controller (see the Preferred Controller option

in Section 2.6.2, 2.6. 4, and 2.6.5 for creating JBOD disk, logical disk, and volume, respectively). When the I/O paths from

host computers to the virtual disk are available and the preferred controller is online, the MPIO driver will dispatch the I/O

to the paths of the preferred controller for the virtual disk.

Tasks Instructions

Create Virtual volumes and specify the preferred

controller

RAID Management > Disk Groups > Create DG0 and DG1

RAID Management > Logical Disks > Create DG0LD0 >

Specify the preferred controller as ctla

RAID Management > Logical Disks > Create DG0LD1 >

Specify the preferred controller as ctla

RAID Management > Logical Disks > Create DG1LD0 >

Specify the preferred controller as ctlb

RAID Management > Logical Disks > Create DG1LD1 >

Specify the preferred controller as ctlb

Select Controller Failover mode Multiple-ID

Select Storage Provisioning method RAID Management > Storage Provisioning > Simple

Specify the LUN ID and map LUNs to fiber ports fcpa1 -> DG0LD1

fcpa2 -> DG0LD0

fcpb1 -> DG1LD1

fcpb2 -> DG1LD0

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