Introducing the SSA RAID Cluster Adapter

Introducing the SSA RAID Cluster Adapter

The IBM SSA RAID Cluster Adapter for PC Servers is a PCI bus-master adapter that serves as the interface between systems using the Peripheral Component Interconnect (PCI) architecture and devices using the Serial Storage Architecture (SSA). The SSA RAID Cluster Adapter provides for RAID-1 arrays and non-RAID disk drives.


SSA is a high-performance serial-interconnect technology used to connect I/O devices and host adapters. SSA is an open standard, and SSA specifications have been approved by the SSA Industry Association and are in the process of being approved as an ANSI standard through the ANSI X3T1O.1 subcommittee. SSA retains the SCSI-2 commands, queuing model, status, and sense bytes.

In SSA subsystems, transmissions to several destinations are multiplexed, the effective bandwidth is further increased by spatial reuse of the individual links. Commands are forwarded automatically from device to device along a loop until the target device is reached. Multiple commands can be travelling around the loop simultaneously.

The Adapter Card

The adapter provides 4 SSA ports for the attachment of storage devices such as hard disk drives. Each port operates at 20 MB/s full-duplex using point-to-point copper cables up to 25 meters long.


On the adapter card, there is a light next to the pair of SSA connectors (port 1 and port 2) for each SSA loop.

On the front panel of the adapter and on one of its modules are labels on which is printed the 15-character SSA unique ID of the adapter.


RAID (Redundant Array of Independent Disks) is the technology of grouping several hard disk drives into an array that is defined as a single logical disk drive. This grouping technique increases data availability, if one disk fails, the system continues to run, with no operator intervention required. The failed disk can be replaced without turning off the server (hot swapping).

The SSA RAID Cluster Adapter provides RAID functions within the interface between your server and its disk drives. Disk drives connected to the adapter can be configured as individual drives, as members of a RAID-1 array, or as hot spares for future use in an array.
The members of an array should be disk drives only, that is, having an array as a member of another array is not supported.

If you need some basic information about RAID technology, refer to, 'Introducing SSA and RAID'


Two SSA RAID Cluster Adapters can be connected in one or two SSA loops with SSA disk drives. This arrangement is known as a cluster. (Neither of the two servers in an SSA cluster can share disk drives with a third server.) One of the adapters is considered the primary adapter By default, this is the adapter with the higher SSA unique ID. There is an option within the configuration utility to select the other adapter as the primary adapter, 'Changing the Primary Adapter' describes how to use this option. The performance of I/O operations to RAID-1 arrays is:

The primary adapter controls all the arrays that are configured on the adapters. Commands for an array from the adapter that is not the primary adapter are routed to the primary adapter to be implemented. Commands for disk drives that are not members of an array are implemented by the adapter in the server that issues the command.

If the non-primary adapter detects that the primary adapter has failed, the non-primary adapter becomes the primary adapter and takes control of all the arrays. This is called failover .

, 'Introducing SSA and RAID' includes more detailed information about the physical configuration needed and the operation of clustered adapters.

Disk Drives Not in Arrays

Access to disk drives that are not members of arrays can be restricted to one of the adapters of a pair. 'Viewing and Changing Disk Drive Access Modes' describes how to do this. Access must be restricted in this way if you want to boot from an SSA disk drive that is attached to clustered adapters.

Operating Systems

The SSA RAID Cluster Adapter, its firmware, and the software supplied with it provide attachments of SSA devices to servers running Microsoft Windows NT 4.0 Server or Microsoft Windows NT 4.0 Server/Enterprise Edition which includes Microsoft Cluster Server.

Microsoft Cluster Server handles failover between clustered adapters. The maximum number of arrays you can define is lower if you are using Microsoft Cluster Server, 'Clustering Implementation' gives details of this.

Before Installing the Adapter

This book is intended for a network administrator-that is, the person responsible for configuring, maintaining, managing, and troubleshooting a PC server. The administrator should be familiar with RAID and hot-swapping technology.

  Do not open the static-protective bag containing the adapter until instructed to do so.

This option package contains:

Installation Requirements

To install this option, you will need the following:

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