PC Server 325 Tower Cluster Example

PC Server 325 Tower Cluster Example

(Below) Figure 2 shows a low-cost, high-availability, shared-disk cluster consisting of two tower models of the PC Server 325 and one PC Server 3518 Enterprise Expansion Enclosure.
In addition to its standard features, each PC Server 325 contains one IBM ServeRAID II Ultra SCSI Adapter, one IBM 100/10 PCI EtherJet Adapter, and one additional 4.51 GB hard disk drive.
(See 'Parts List for the PC Server 325 Tower Cluster Example' for a complete list of the components used in this example.)

Note: Although this example shows ServeRAID II adapters, you also could use ServeRAID-3H adapters.

Figure 2. PC Server 325 Tower Cluster Example

This figure represents raw-storage capacity. Several factors influence the actual amount of useable-storage capacity, such as the drive's capacity and the RAID levels assigned.

The network-crossover cable, sometimes referred to as the cluster's heartbeat, provides the dedicated, point-to-point communication link between the servers.
This cable connects the IBM 100/10 PCI EtherJet Adapters (one in each server) and enables the servers to continuously monitor each other's functional status.
The servers connect to the public network using the Ethernet controllers on the system boards.
Using the public-network connection and the dedicated heartbeat link together ensures that a single network-hardware failure will not initiate a failover situation.

Notes:

You must use IBM 100/10 PCI EtherJet Adapters for the cluster's heartbeat connection.
You can use the integrated Ethernet controllers that come standard on some server models to connect the server to the public network, however, these integrated controllers are not certified for use as the cluster's heartbeat connection.
You must use a point-to-point, Category 5 crossover cable for the heartbeat connection. Connections through a hub are not supported.

To maintain high availability, the two hard disk drives in each server are defined as RAID level-1 logical drives (Array A) using Channel 2 of the ServeRAID adapters. Because these nonshared drives store the operating system and shared-disk clustering software needed during startup, these drives were defined first using the ServeRAID configuration program.

The internal SCSI cables remain attached to the CD-ROM drives, but the end connectors that were attached to the SCSI controllers on the system boards are now attached to the Channel 2 connectors on the ServeRAID adapters. The hard disk drive attached to the end connector on the internal SCSI cable in each server has its termination set to Enabled. The other hard disk drive in each server has its termination set to Disabled.

Note: The termination for the CD-ROM drive is permanently set to Disabled. You can not Enable termination on the CD-ROM drive.

The only difference between the hardware configuration of Server A and the hardware configuration of Server B is the SCSI ID settings for the ServeRAID adapters. Channels 1 and 2 of the ServeRAID adapter in Server A are set to SCSI ID 7. Channel 1 of the ServeRAID adapter in Server B is set to SCSI ID 6, because it shares the same SCSI bus as Channel 1 of the ServeRAID adapter in Server A. Channel 2 of the ServeRAID adapter in Server B connects to the nonshared drives and is set to SCSI ID 7 to avoid a conflict with the CD-ROM drive, which is set to SCSI ID 6. On both ServeRAID adapters, Channel 3 is available for use as a quorum-arbitration link with the Microsoft Cluster Server software, or for future expansion with the Vinca clustering software.

In addition to the standard features of the PC Server 3518, the expansion enclosure contains a power-supply upgrade option, an additional backplane, two enhanced SCSI repeaters, and cables. The maximum achievable hot-swap storage capacity 3 for this enclosure is 163.8 GB using eighteen 9.1 GB drives. However, this example shows only eight drives, which leaves space for future expansion.

To help maintain high availability, the eight hard disk drives are defined as two RAID level-5 logical drives (arrays B and C). To further increase the availability of these shared drives, each ServeRAID adapter has its own hot-spare (HSP) drive. A hot-spare drive is a disk drive that is defined for automatic use in the event of a drive failure. If a physical drive fails and it is part of a RAID level-1 or RAID level-5 logical drive, the ServeRAID adapter will automatically start to rebuild the data on the hot-spare drive.

Note: ServeRAID adapters cannot share hot-spare drives. To maintain high availability and enable the automatic-rebuild feature, you must define a hot-spare drive for each ServeRAID adapter. The jumpers on the backplane in Bank D are set for Bank D and for high addressing (SCSI IDs 8, 9, 10, 11, 12, and 13). A cable connects the Bank C and Bank D backplanes, creating one continuous SCSI bus.

Channel 1 of the ServeRAID adapter in Server A connects to the enhanced SCSI repeater that connects to Bank C, and Channel 1 of the ServeRAID adapter in Server B connects to the enhanced SCSI repeater that connects to Bank D. The enhanced SCSI repeaters contain circuits that can automatically sense the functional status of the server. When the SCSI repeater circuitry detects that the server attached to it is failing or offline, the SCSI repeater automatically enables termination for that end of the SCSI bus. This helps increase the availability of the shared disks and enables the serviceability of the failing or offline server.

Ideally, the servers and storage enclosures are connected to different electrical circuits, however, this is rarely possible. To help prevent the loss of data and to maintain the availability of the shared disks during a power outage or power fluctuation, always connect the servers and expansion enclosures to uninterruptible power supplies (UPS).

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