HP OpenVMS Systems Documentation

A "hot" file is a file in your system on which the most activity occurs. Hot files exist because, in many environments, approximately 80% of all I/O goes to 20% of data. This means that, of equal regions on a disk drive, 80% of the data being transferred goes to one place on a disk, as shown in Figure 9-12.

Figure 9-12 Hot-File Distribution

To increase the scalability of I/Os, focus on hot files, which can become a bottleneck if you do not manage them well. The activity in this area is expressed in I/Os, megabytes transferred, and queue depth.

RAID level 0 balances hot-file activity by spreading a single file over multiple disks. This reduces the performance impact of hot files.

Use the following DCL commands to analyze hot-file activity:

• MONITOR IO command---Monitors hot disks.
• MONITOR MSCP command---Monitors MSCP servers.

The MONITOR IO and the MONITOR MSCP commands enable you to find out which disk and which server are hot.

9.5.7 Volume Shadowing

The Volume Shadowing for OpenVMS product ensures that data is available to applications and end users by duplicating data on multiple disks. Although volume shadowing provides data redundancy and high availability, it can affect OpenVMS Cluster I/O on two levels:

This chapter suggests some key system management strategies that you can use to get the most out of your OpenVMS Cluster. It is not intended to be a comprehensive discussion of the most common OpenVMS Cluster system management practices; see HP OpenVMS Cluster Systems for that information.

This chapter also assumes that the reader has some familiarity with basic system management concepts, such as system disks, quorum disks, and OpenVMS Cluster transitions.

The following information is contained in this chapter:

• System disk strategies
• Common and multiple environment strategies
• Quorum strategies
• State transition strategies
• Multiple OpenVMS versions in the same OpenVMS Cluster
• Multiple platforms (Integrity servers and Alpha systems in the same OpenVMS Cluster

OpenVMS Cluster software makes a system manager's job easier because many system management tasks need to be done only once. This is especially true if business requirements call for a simple configuration rather than for every feature that an OpenVMS Cluster can provide. The simple configuration is appealing to both new and experienced system managers and is applicable to small OpenVMS Clusters---those with 3 to 7 nodes, 20 to 30 users, and 100 GB of storage.

Complex OpenVMS Cluster configurations may require a more sophisticated system management strategy to deliver more availability, scalability, and performance.

Reference: See Figure 10-2 for an example of a complex OpenVMS Cluster configuration.

Choose system management strategies that balance simplicity of system management with the additional management tasks required by more complex OpenVMS Clusters.

10.2 System Disk Strategies

System disks contain system files and environment files.

System files are primarily read-only images and command procedures, such as run-time libraries, and are accessed clusterwide.

Environment files create specific working environments for users. You can create a common environment by making all environment files accessible clusterwide, or you can create multiple environments by making specific environment files accessible to only certain users or systems.

10.2.1 Single System Disk

System management is easiest for a simple configuration that has a single system disk and a common environment. Most procedures need to be performed only once, and both system files and environment files are located on the same disk. Page and swap files are also located on the system disk.

Figure 10-1 shows another variation of a simple OpenVMS Cluster with a common environment.

Figure 10-1 Simple LAN OpenVMS Cluster with a Single System Disk

In Figure 10-1, six satellites and one boot server are connected by Ethernet. Each satellite has its own page and swap disk, which saves system disk space and removes the I/O activity of page and swap files from the Ethernet. Removing page and swap files from the system disk improves performance for the OpenVMS Cluster.

Although the single-system-disk configuration works well for many OpenVMS Cluster requirements, multiple system disks can offer several advantages.

10.2.2 Multiple System Disks

OpenVMS Clusters that include both Integrity servers and Alpha systems require multiple system disks: an Integrity server system disk and an Alpha system disk. Table 10-1 gives some additional reasons (not related to architecture) why a system manager might want more than one system disk in a OpenVMS Cluster.

10.2.3 Multiple System-Disk OpenVMS Cluster

Figure 10-2 Multiple System Disks in a Common Environment

Figure 10-2 is an OpenVMS Cluster with multiple system disks:

• One for Alpha 1, Alpha 2, and Alpha 3
• One for each boot server on the LAN segments

The use of multiple system disks in this configuration and the way that the LAN segments are divided enable the booting sequence to be efficient and timely.

10.2.4 Dividing an OpenVMS Cluster System

In the workstation server examples shown in Section 9.3, OpenVMS Cluster reboots after a failure are relatively simple because of the small number of satellites per server. However, reboots in the larger, OpenVMS Cluster configuration shown in Figure 10-2 require careful planning. Dividing this OpenVMS Cluster and arranging the system disks as described in this section can reduce booting time significantly. Dividing the OpenVMS Cluster can also reduce the satellite utilization of the LAN segment and increase satellite performance.

The disks in this OpenVMS Cluster have specific functions, as described in Table 10-2.

In a booting sequence for the configuration in Figure 10-2, make sure that nodes Alpha 1, Alpha 2, and Alpha 3 are entirely booted before booting the LAN Ethernet segments so that the files on the common disk are available to the satellites. For FDDI configuration, enable filtering of the Maintenance Operations Protocol (MOP) on the Ethernet-to-FDDI (10/100) bridges so that the satellites do not try to boot from the system disks for Alpha 1, Alpha 2, and Alpha 3. The order in which to boot this OpenVMS Cluster is:

1. Boot Alpha 1, Alpha 2, and Alpha 3.
2. Boot the satellite boot servers.
3. Boot all satellites.

Reference: See Section 9.3.7 for information about extended LANs.

10.2.5 Summary: Single Versus Multiple System Disks

Use the information in Table 10-3 to determine whether you need a system disk for the entire OpenVMS Cluster or multiple system disks.

Depending on your processing needs, you can prepare either a common environment, in which all environment files are shared clusterwide, or a multiple environment, in which some files are shared clusterwide and others are accessible only by certain OpenVMS Cluster members.

The following are the most frequently used and manipulated OpenVMS Cluster environment files:

SYS$SYSTEM:SYSUAF.DAT
SYS$SYSTEM:NETPROXY.DAT
SYS$SYSTEM:VMSMAIL_PROFILE.DATA
SYS$SYSTEM:NETNODE_REMOTE.DAT
SYS$MANAGER:NETNODE_UPDATE.COM
SYS$SYSTEM:RIGHTSLIST.DAT
SYS$SYSTEM:QMAN$MASTER.DAT

Reference: For more information about managing these files, see HP OpenVMS Cluster Systems.

10.3.1 Common Environment

A common OpenVMS Cluster environment is an operating environment that is identical on all nodes in the OpenVMS Cluster. A common environment is easier to manage than multiple environments because you use a common version of each system file. The environment is set up so that:

• All nodes run the same programs, applications, and utilities.
• All users have the same type of accounts, and the same logical names are defined.
• All users can have common access to storage devices and queues.
• All users can log in to any node in the configuration and can work in the same environment as all other users.

The simplest and most inexpensive environment strategy is to have one system disk for the OpenVMS Cluster with all environment files on the same disk. The benefits of this strategy are:

• Software products need to be installed only once.
• All environment files are on the system disk and are easier to locate and manage.
• Booting dependencies are clear.

For an OpenVMS Cluster in which every node share the same system disk and environment, most common environment files are located in the SYS$SYSTEM directory.

However, you may want to move environment files to a separate disk so that you can improve OpenVMS Cluster performance. Because the environment files typically experience 80% of the system-disk activity, putting them on a separate disk decreases activity on the system disk. Figure 10-2 shows an example of a separate, common disk.

If you move environment files such as SYSUAF.DAT to a separate, common disk, SYSUAF.DAT will not be located in its default location of SYS$SYSTEM:SYSUAF.DAT.

Reference: See HP OpenVMS Cluster Systems for procedures to ensure that every node in the OpenVMS Cluster can access SYSUAF.DAT in its new location.

10.3.3 Multiple Environments

Multiple environments can vary from node to node. You can set up an individual node or a subset of nodes to:

• Provide multiple access according to the type of tasks users perform and the resources they use.
• Share a set of resources that are not available on other nodes.
• Perform specialized functions using restricted resources while other processors perform general timesharing work.
• Allow users to work in environments that are specific to the node where they are logged in.

Figure 10-3 shows an example of a multiple environment.

Figure 10-3 Multiple-Environment OpenVMS Cluster

In Figure 10-3, the multiple-environment OpenVMS Cluster consists of two system disks: one for Integrity server nodes and one for Alpha nodes. The common disk contains environment files for each node or group of nodes. Although many OpenVMS Cluster system managers prefer the simplicity of a single (common) environment, duplicating environment files is necessary for creating multiple environments that do not share resources across every node. Each environment can be tailored to the types of tasks users perform and the resources they use, and the configuration can have many different applications installed.

Each of the four Fibre Channel nodes has its own page and swap disk, offloading the Alpha and Integrity server system disks on the FC interconnect from page and swap activity. All of the disks are shadowed across the FC interconnects, which protects the disks if a failure occurs.

10.4 Additional Multiple-Environment Strategies

This section describes additional multiple-environment strategies, such as using multiple SYSUAF.DAT files and multiple queue managers.

10.4.1 Using Multiple SYSUAF.DAT Files

Most OpenVMS Clusters are managed with one user authorization (SYSUAF.DAT) file, but you can use multiple user authorization files to limit access for some users to certain systems. In this scenario, users who need access to all systems also need multiple passwords.

Be careful about security with multiple SYSUAF.DAT files. The OpenVMS Integrity servers and OpenVMS Alpha operating systems do not support multiple security domains.

Reference: See HP OpenVMS Cluster Systems for the list of fields that need to be the same for a single security domain, including SYSUAF.DAT entries.

Because Alpha systems require higher process quotas, system managers often respond by creating multiple SYSUAF.DAT files. This is not an optimal solution. Multiple SYSUAF.DAT files are intended only to vary environments from node to node, not to increase process quotas. To increase process quotas, HP recommends that you have one SYSUAF.DAT file and that you use system parameters to override process quotas in the SYSUAF.DAT file with system parameters to control resources for your Alpha systems.

10.4.2 Using Multiple Queue Managers

If the number of batch and print transactions on your OpenVMS Cluster is causing congestion, you can implement multiple queue managers to distribute the batch and print loads between nodes.

Every OpenVMS Cluster has only one QMAN$MASTER.DAT file. Multiple queue managers are defined through multiple *.QMAN$QUEUES and *.QMAN$JOURNAL files. Place each pair of queue manager files on different disks. If the QMAN$MASTER.DAT file has contention problems, place it on a solid-state disk to increase the number of batch and print transactions your OpenVMS Cluster can process. For example, you can create separate queue managers for batch queues and print queues.

Reference: See OpenVMS System Manager's Manual, Volume 1: Essentials for examples and commands to implement multiple queue managers.

10.5 Quorum Strategies

OpenVMS Cluster systems use a quorum algorithm to ensure synchronized access to storage. The quorum algorithm is a mathematical method for determining whether a majority of OpenVMS Cluster members exists so that they can "vote" on how resources can be shared across an OpenVMS Cluster system. The connection manager, which calculates quorum as a dynamic value, allows processing to occur only if a majority of the OpenVMS Cluster members are functioning.

Quorum votes are contributed by:

• Systems with the parameter VOTES set to a number greater than zero
• A designated disk, called a quorum disk

Each OpenVMS Cluster system can include only one quorum disk. The disk cannot be a member of a shadow set, but it can be the system disk.

The connection manager knows about the quorum disk from "quorum disk watchers," which are any systems that have a direct, active connection to the quorum disk.

10.5.1 Quorum Strategy Options

At least two systems should have a direct connection to the quorum disk. This ensures that the quorum disk votes are accessible if one of the systems fails.

When you consider quorum strategies, you must decide under what failure circumstances you want the OpenVMS Cluster to continue. Table 10-4 describes four options from which to choose.

Reference: For more information about quorum disk management, see HP OpenVMS Cluster Systems.