NT Cluster-in-a-Box

Wouldn't you like to guarantee users 100 percent uptime? Database users would never have to worry about the system going down, you could guarantee 24-hour-a-day availability for your e-commerce systems, and you'd get that big promotion for making it all happen. That guarantee is the Holy Grail of clustering.

Big Iron
Data General's entry into the Windows NT clustering market is NT Cluster-in-a-Box. The case is reminiscent of midrange computers of years past: The unit measures 28"*36"*60" and houses two Quad 200MHz Pentium Pro motherboards, 1.5GB of RAM, two 2GB Barracuda hard disks, an 18GB CLARiiON RAID array, Error-Correcting Code (ECC) memory, and a split SCSI bus. You can order the system with disk arrays capable of holding either 20 or 30 disks, which also support the 2GB, 4GB, and 9GB drives, for a maximum of 270GB.

NT Cluster-in-a-Box comes with four 4-port OSICOM (formerly RNS) LAN cards for a total of sixteen 10/100Mbps autosense ports, and two 33.6Kbps modems for remote access. Top this configuration off with a rack-mounted Apex Outlook video, keyboard, and mouse switch and a 17" monitor all fed by two 30 amp 220 volt power feeds. But wait; there's more: The whole unit is rack-mounted with factory-completed cabling, dual power supplies for the individual systems, enhanced cooling within the individual systems, and dual 220 volt power feed internal power buses. The CLARiiON disk array includes dual storage processors, fault tolerant disk array technology (using RAID 1 and RAID 5 and supporting other RAID levels), N+1 (where N = number needed for operation) power and cooling, repair-under-power features, and a battery-backed-up 8MB write cache per storage processor (with a maximum of 64MB per processor). Add all these features up, and you are dealing with more than an enterprise-class NT machine.

How Does It Work?
Enough with the hardware. In this review, I want to determine how well this unit does as a clustering solution. Think of the Cluster-in-a-Box as two separate systems connected via Ethernet. The Fast/Wide SCSI controllers are configured as a split bus--each system's SCSI bus terminates at the storage processor in the CLARiiON. This configuration provides service to one clustered system's connection without interruption to the other clustered system and doesn't allow a total failure if a SCSI cable comes off and breaks the SCSI bus. The system can run in the shared bus mode (and will have to for Wolfpack). Each system can function independently of the other and can run any standard NT applications. Data General's intent is to have each system doing meaningful work. System A can be a primary SQL Server machine and System B can be a primary Web machine. Each machine can be the primary backup for the other. So System A backs up the Web server and System B backs up the SQL Server. The system comes completely configured and ready to go, right out of the crate (that's right, crate).

By default, the system is configured as a symmetric cluster. The CLARiiON RAID array is divided into three partitions: The first is a 2GB partition (a RAID 1 mirrored pair) designated drive T. The second partition, V, is an 8.3GB RAID 5 partition. The third partition, U, is a 2GB RAID 1 mirrored pair. Partitions T and V are available to the primary system, named AViiONA. Partition U is available to the second system in the cluster, AViiONB. Each system also has a 2GB Seagate Barracuda drive to load operating systems and other applications. The CLARiiON RAID array is primarily for sharing data. All the RAID drives are hardware RAID, not the slower software-based RAID NT provides.

By default, the CLARiiON RAID array transfers control of drives T and V to the AViiONB system if the AViiONA system fails. After the AViiONA, or primary system, comes back online, AViiONB returns control of drives T and V to AViiONA. The two systems continuously communicate their respective status to each other. They conduct this communication with two Ethernet connections per machine. These links, known as heartbeats, keep each of two systems in the cluster in contact with the other.

For this review I tested how well NT Cluster-in-a-Box handles SQL Server in a clustered environment. I installed SQL Server on both systems in the cluster. I used an HP NetServer LX Pro and Bluecurve's Dynameasure software to simulate 100 SQL users pounding away on AViiONA. In the middle of the simulation, I cut power to AViiONA and checked whether AViiONB took over without the users knowing anything had happened.

VERITAS FirstWatch
NT Cluster-in-a-Box uses third-party clustering software by VERITAS. FirstWatch is available from VERITAS on NT and UNIX platforms separately. I tested VERITAS FirstWatch with CLARiiON support added. FirstWatch uses agents to transfer control of disk drives and services between systems in the cluster. NT Cluster-in-a-Box comes with the VERITAS clustering software installed. All you have to do is assign IP addresses to the network cards on either system, and you're ready to go. Figure 1 shows system configuration for NT Cluster-in-a-Box with VERITAS FirstWatch software.

I recommend that you read the manual. Although clustering seems simple in theory, it is very complex in practice. The VERITAS software is a UNIX port that is not yet fully integrated with NT. The result is a mix of Windows programs and text GUI programs. The manual contains all the information you will need to configure VERITAS for SQL clustering, but it is very terse and difficult to read. If you invest the money for NT Cluster-in-a-Box, spend extra for a support contract.