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HP OpenVMS Cluster Systems

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9.5.3 Defining the Satellite System to the Boot Server

Integrity server Satellite systems boot via the PXE protocol. On OpenVMS, PXE is handled by BOOTP from the TCPIP product. If you are using more than one Integrity server system, which is a boot server in your cluster, be sure the BOOTP database is on a common disk. See the TCPIP documentation for information on configuring TCPIP components. TCPIP must be installed, configured and running before attempting to define a satellite system.

On an Integrity server system, which is a boot server, log in to the system manager's or other suitably privileged account. Execute the command procedure SYS$MANAGER:CLUSTER_CONFIG_ LAN.COM. (CLUSTER_CONFIG.COM, which configures satellite nodes using DECnet, does not support Integrity server systems. It will, however, automatically invoke CLUSTER_CONFIG_LAN for Integrity server systems.) CLUSTER_CONFIG_LAN is a menudriven command procedure designed to help you configure satellite systems. The menus are context-sensitive and may vary depending on architecture and installed products. If you are unfamiliar with the procedure, please see refer to the System Management documentation for a more extensive overview of CLUSTER_CONFIG_LAN.

The essential information required to add an Integrity server satellite includes the node's SCS node name, SCS system ID, and hardware address. In addition, you will need to know the satellite's IP address, network mask, and possibly gateway addresses. If you are unfamiliar with these concepts, please refer to the TCPIP documentation. The procedure will create a system root for the satellite.

CLUSTER_CONFIG_LAN should perform all steps required to make the satellite system bootable. If you choose local paging and swapping files, you will be prompted to boot the satellite system into the cluster so that the files may be created. If not, paging and swapping files will be created on the served system disk and you may boot the satellites at your convenience.

9.5.4 Booting the Satellite

If you have previously added an option to the boot menu, select that option. If you have not, see your hardware documentation for the steps required to boot from a network adapter. Be sure to set the environment variable VMS_FLAGS to include the memory disk boot flag (0x200000). The system will detail boot progress in the form of a system message when VMS_LOADER is obtained from the network, followed by one period character written to the console device for every file downloaded to start the boot sequence and last by a message indicating that IPB (the primary bootstrap image) has been loaded.

Note the following example:

Loading.: Satellite Boot EIA0 Mac(00-13-21-5b-86-48) 
Running LoadFile() 
CLIENT MAC ADDR: 00 13 21 5B 86 48 
TSize.Running LoadFile() 
Starting: Satellite Boot EIA0 Mac(00-13-21-5b-86-48) 
Loading memory disk from IP 
Loading file: $13$DKA0:[SYS10.SYSCOMMON.SYSEXE]IPB.EXE from IP 
%IPB-I-SATSYSDIS, Satellite boot from system device $13$DKA0: 
HP OpenVMS Industry Standard 64 Operating System, Version V8.3 
© Copyright 1976-2006 Hewlett-Packard Development Company, L.P. 

Upon first full boot, the satellite system will run AUTOGEN and reboot.

9.5.5 Additional Tasks on the Satellite System

If you had not done so previously, create the dump file for DOSD at this time. Edit the SYS$STARTUP:SYCONFIG.COM file and add commands to mount the DOSD device. In order for the error log buffers to be recovered, the DOSD device must be mounted in SYCONFIG.

9.6 Booting Satellites with IP interconnect (Integrity servers, Alpha)

For Alpha satellite nodes, the satellite node and its boot server must exist in the same LAN segment. To select the interface to be used for satellite booting, assume that the satellite node does not have any disk running OpenVMS connected to it. If you are adding Alpha systems as satellite nodes, you can receive information from the ">>>" prompt by executing the following command:

P00>>>show device 
dga5245.1003.0.3.0         $1$DGA5245   COMPAQ HSV110 (C)COMPAQ  3028 
dga5245.1004.0.3.0         $1$DGA5245   COMPAQ HSV110 (C)COMPAQ  3028 
dga5890.1001.0.3.0         $1$DGA5890   COMPAQ HSV110 (C)COMPAQ  3028 
dga5890.1002.0.3.0         $1$DGA5890   COMPAQ HSV110 (C)COMPAQ  3028 
dka0.0.0.2004.0            DKA0              COMPAQ BD03685A24  HPB7 
dka100.1.0.2004.0          DKA100            COMPAQ BD01864552  3B08 
dka200.2.0.2004.0          DKA200            COMPAQ BD00911934  3B00 
dqa0.              DQA0       HL-DT-ST CD-ROM GCR-8480  2.11 
dva0.0.0.1000.0            DVA0 
eia0.0.0.2005.0            EIA0              00-06-2B-03-2D-7D 
pga0.               PGA0        WWN 1000-0000-c92a-78e9 
pka0.7.0.2004.0            PKA0                  SCSI Bus ID 7 
pkb0.               PKB0                  SCSI Bus ID 6  5.57 

From the output, the LAN interface will be EIA0 on which the IP address will be configured and used for Cluster configuration.


The Alpha console uses the MOP protocol for network load of satellite systems. Since the MOP protocol is non-routable, the satellite boot server or servers and all satellites booting from them must reside in the same LAN. In addition, the boot server must have at least one LAN device enabled for cluster communications to permit the Alpha satellite nodes to access the system disk.

On Integrity server systems, the interface name will either start with EI or EW. If it is the first interface, it will be EIA0 or EWA0. Note the mac address of the interface that you want to use from the Shell prompt. To obtain the interface information on Integrity servers, execute the following command on the EFI Shell:

Shell> lanaddress 
LAN Address Information 
   LAN Address        Path 
   -----------------  ---------------------------------------- 
   Mac(00306E4A133F)  Acpi(HWP0002,0)/Pci(3|0)/Mac(00306E4A133F)) 
  *Mac(00306E4A02F9)  Acpi(HWP0002,100)/Pci(2|0)/Mac(00306E4A02F9)) 

Assuming that the active interface is EIA0, configure the satellite with EIA0, if it does not boot with EIA0 try with EWA0 subsequently. For more information about configuring a satellite node, see Section

9.7 System-Disk Throughput

Achieving enough system-disk throughput requires some combination of the following techniques:

Technique Reference
Avoid disk rebuilds at boot time. Section 9.7.1
Offload work from the system disk. Section 9.7.2
Configure multiple system disks. Section 9.7.3
Use Volume Shadowing for OpenVMS. Section 6.6

9.7.1 Avoiding Disk Rebuilds

The OpenVMS file system maintains a cache of preallocated file headers and disk blocks. When a disk is not properly dismounted, such as when a system fails, this preallocated space becomes temporarily unavailable. When the disk is mounted again, OpenVMS scans the disk to recover that space. This is called a disk rebuild.

A large OpenVMS Cluster system must ensure sufficient capacity to boot nodes in a reasonable amount of time. To minimize the impact of disk rebuilds at boot time, consider making the following changes:

Action Result
Use the DCL command MOUNT/NOREBUILD for all user disks, at least on the satellite nodes. Enter this command into startup procedures that mount user disks. It is undesirable to have a satellite node rebuild the disk, yet this is likely to happen if a satellite is the first to reboot after it or another node fails.
Set the system parameter ACP_REBLDSYSD to 0, at least for the satellite nodes. This prevents a rebuild operation on the system disk when it is mounted implicitly by OpenVMS early in the boot process.
Avoid a disk rebuild during prime working hours by using the SET VOLUME/REBUILD command during times when the system is not so heavily used. Once the computer is running, you can run a batch job or a command procedure to execute the SET VOLUME/REBUILD command for each disk drive. User response times can be degraded during a disk rebuild operation because most I/O activity on that disk is blocked. Because the SET VOLUME/REBUILD command determines whether a rebuild is needed, the job can execute the command for every disk. This job can be run during off hours, preferably on one of the more powerful nodes.

Caution: In large OpenVMS Cluster systems, large amounts of disk space can be preallocated to caches. If many nodes abruptly leave the cluster (for example, during a power failure), this space becomes temporarily unavailable. If your system usually runs with nearly full disks, do not disable rebuilds on the server nodes at boot time.

9.7.2 Offloading Work

In addition to the system disk throughput issues during an entire OpenVMS Cluster boot, access to particular system files even during steady-state operations (such as logging in, starting up applications, or issuing a PRINT command) can affect response times.

You can identify hot system files using a performance or monitoring tool (such as those listed in Section 1.5.2), and use the techniques in the following table to reduce hot file I/O activity on system disks:

Potential Hot Files Methods to Help
Page and swap files When you run CLUSTER_CONFIG_LAN.COM or CLUSTER_CONFIG.COM to add computers to specify the sizes and locations of page and swap files, relocate the files as follows:
  • Move page and swap files for computers off system disks.
  • Set up page and swap files for satellites on the satellites' local disks, if such disks are available.
Move these high-activity files off the system disk:
  • Layered product and other application files
Use any of the following methods:
  • Specify new locations for the files according to the instructions in Chapter 5.
  • Use caching in the HSC subsystem or in RF or RZ disks to improve the effective system-disk throughput.
  • Add a solid-state disk to your configuration. These devices have lower latencies and can handle a higher request rate than a regular magnetic disk. A solid-state disk can be used as a system disk or to hold system files.
  • Use DECram software to create RAMdisks on MOP servers to hold copies of selected hot read-only files to improve boot times. A RAMdisk is an area of main memory within a system that is set aside to store data, but it is accessed as if it were a disk.

Moving these files from the system disk to a separate disk eliminates most of the write activity to the system disk. This raises the read/write ratio and, if you are using Volume Shadowing for OpenVMS, maximizes the performance of shadowing on the system disk.

9.7.3 Configuring Multiple System Disks

Depending on the number of computers to be included in a large cluster and the work being done, you must evaluate the tradeoffs involved in configuring a single system disk or multiple system disks.

While a single system disk is easier to manage, a large cluster often requires more system disk I/O capacity than a single system disk can provide. To achieve satisfactory performance, multiple system disks may be needed. However, you should recognize the increased system management efforts involved in maintaining multiple system disks.

Consider the following when determining the need for multiple system disks:

  • Concurrent user activity
    In clusters with many satellites, the amount and type of user activity on those satellites influence system-disk load and, therefore, the number of satellites that can be supported by a single system disk. For example:
    IF... THEN... Comments
    Many users are active or run multiple applications simultaneously The load on the system disk can be significant; multiple system disks may be required. Some OpenVMS Cluster systems may need to be configured on the assumption that all users are constantly active. Such working conditions may require a larger, more expensive OpenVMS Cluster system that handles peak loads without performance degradation.
    Few users are active simultaneously A single system disk might support a large number of satellites. For most configurations, the probability is low that most users are active simultaneously. A smaller and less expensive OpenVMS Cluster system can be configured for these typical working conditions but may suffer some performance degradation during peak load periods.
    Most users run a single application for extended periods A single system disk might support a large number of satellites if significant numbers of I/O requests can be directed to application data disks. Because each workstation user in an OpenVMS Cluster system has a dedicated computer, a user who runs large compute-bound jobs on that dedicated computer does not significantly affect users of other computers in the OpenVMS Cluster system. For clustered workstations, the critical shared resource is a disk server. Thus, if a workstation user runs an I/O-intensive job, its effect on other workstations sharing the same disk server might be noticeable.
  • Concurrent booting activity
    One of the few times when all OpenVMS Cluster computers are simultaneously active is during a cluster reboot. All satellites are waiting to reload the operating system, and as soon as a boot server is available, they begin to boot in parallel. This booting activity places a significant I/O load on the boot server, system disk, and interconnect.
    Note: You can reduce overall cluster boot time by configuring multiple system disks and by distributing system roots for computers evenly across those disks. This technique has the advantage of increasing overall system disk I/O capacity, but it has the disadvantage of requiring additional system management effort. For example, installation of layered products or upgrades of the OpenVMS operating system must be repeated once for each system disk.
  • System management
    Because system management work load increases as separate system disks are added and does so in direct proportion to the number of separate system disks that need to be maintained, you want to minimize the number of system disks added to provide the required level of performance.

Volume Shadowing for OpenVMS is an alternative to creating multiple system disks. Volume shadowing increases the read I/O capacity of a single system disk and minimizes the number of separate system disks that have to be maintained because installations or updates need only be applied once to a volume-shadowed system disk. For clusters with substantial system disk I/O requirements, you can use multiple system disks, each configured as a shadow set.

Cloning the system disk is a way to manage multiple system disks. To clone the system disk:

  • Create a system disk (or shadow set) with roots for all OpenVMS Cluster nodes.
  • Use this as a master copy, and perform all software upgrades on this system disk.
  • Back up the master copy to the other disks to create the cloned system disks.
  • Change the volume names so they are unique.
  • If you have not moved system files off the system disk, you must have the SYLOGICALS.COM startup file point to system files on the master system disk.
  • Before an upgrade, be sure to save any changes you need from the cloned disks since the last upgrade, such as MODPARAMS.DAT and AUTOGEN feedback data, accounting files for billing, and password history.

9.8 Conserving System Disk Space

The essential files for a satellite root take up very little space, so that more than 96 roots can easily fit on a single system disk. However, if you use separate dump files for each satellite node or put page and swap files for all the satellite nodes on the system disk, you quickly run out of disk space.

9.8.1 Techniques

To avoid running out of disk space, set up common dump files for all the satellites or for groups of satellite nodes. For debugging purposes, it is best to have separate dump files for each MOP and disk server. Also, you can use local disks on satellite nodes to hold page and swap files, instead of putting them on the system disk. In addition, move page and swap files for MOP and disk servers off the system disk.

Reference: See Section 10.7 to plan a strategy for managing dump files.

9.9 Adjusting System Parameters

As an OpenVMS Cluster system grows, certain data structures within OpenVMS need to grow in order to accommodate the large number of nodes. If growth is not possible (for example, because of a shortage of nonpaged pool) this will induce intermittent problems that are difficult to diagnose. HP recommends you to have a separate network for cluster communication. This can help avoid any user data interference with cluster traffic and suitable for environment that has high intra-cluster traffic.

You should run AUTOGEN with FEEDBACK frequently as a cluster grows, so that settings for many parameters can be adjusted. Refer to Section 8.7 for more information about running AUTOGEN.

In addition to running AUTOGEN with FEEDBACK, you should check and manually adjust the following parameters:


SCS connections are now allocated and expanded only as needed, up to a limit of 65,000.

9.9.1 The SCSRESPCNT Parameter

Description: The SCSRESPCNT parameter controls the number of response descriptor table (RDT) entries available for system use. An RDT entry is required for every in-progress message exchange between two nodes.

Symptoms of entry shortages: A shortage of entries affects performance, since message transmissions must be delayed until a free entry is available.

How to determine a shortage of RDT entries: Use the SDA utility as follows to check each system for requests that waited because there were not enough free RDTs.

8044DF74:  00000000   "...."

How to resolve shortages: If the SDA EXAMINE command displays a nonzero value, RDT waits have occurred. If you find a count that tends to increase over time under normal operations, increase SCSRESPCNT.

9.9.2 The CLUSTER_CREDITS Parameter

Description: The CLUSTER_CREDITS parameter specifies the number of per-connection buffers a node allocates to receiving VMS$VAXcluster communications. This system parameter is not dynamic; that is, if you change the value, you must reboot the node on which you changed it.

Default: The default value is 10. The default value may be insufficient for a cluster that has very high locking rates.

Symptoms of cluster credit problem: A shortage of credits affects performance, since message transmissions are delayed until free credits are available. These are visible as credit waits in the SHOW CLUSTER display.

How to determine whether credit waits exist: Use the SHOW CLUSTER utility as follows:

  4. Type SET CR_WAIT/WIDTH=10.
  5. Check to see whether the number of CR_WAITS (credit waits) logged against the VMS$VAXcluster connection for any remote node is incrementing regularly. Ideally, credit waits should not occur. However, occasional waits under very heavy load conditions are acceptable.

How to resolve incrementing credit waits:

If the number of CR_WAITS is incrementing more than once per minute, perform the following steps:

  1. Increase the CLUSTER_CREDITS parameter on the node against which they are being logged by five. The parameter should be modified on the remote node, not on the node which is running SHOW CLUSTER.
  2. Reboot the node.

Note that it is not necessary for the CLUSTER_CREDITS parameter to be the same on every node.

9.10 Minimize Network Instability

Network instability also affects OpenVMS Cluster operations. Table 9-8 lists techniques to minimize typical network problems.

Table 9-8 Techniques to Minimize Network Problems
Technique Recommendation
Adjust the RECNXINTERVAL parameter. The RECNXINTERVAL system parameter specifies the number of seconds the OpenVMS Cluster system waits when it loses contact with a node, before removing the node from the configuration. Many large OpenVMS Cluster configurations operate with the RECNXINTERVAL parameter set to 40 seconds (the default value is 20 seconds).

Raising the value of RECNXINTERVAL can result in longer perceived application pauses, especially when the node leaves the OpenVMS Cluster system abnormally. The pause is caused by the connection manager waiting for the number of seconds specified by RECNXINTERVAL.

Protect the network For clusters connected on the LAN interconnect, treat the LAN as if it were a part of the OpenVMS Cluster system. For example, do not allow an environment in which a random user can disconnect a ThinWire segment to attach a new PC while 20 satellites hang.

For Clusters running on IP interconnect, ensure that the IP network is protected using a VPN type of security.

Choose your hardware and configuration carefully. Certain hardware is not suitable for use in a large OpenVMS Cluster system.
  • Some network components can appear to work well with light loads, but are unable to operate properly under high traffic conditions. Improper operation can result in lost or corrupted packets that will require packet retransmissions. This reduces performance and can affect the stability of the OpenVMS Cluster configuration.
  • Beware of bridges that cannot filter and forward at full line rates and repeaters that do not handle congested conditions well.
  • Refer to Guidelines for OpenVMS Cluster Configurations to determine appropriate OpenVMS Cluster configurations and capabilities.
Use the LAVC$FAILURE_ANALYSIS facility. See Section D.5 for assistance in the isolation of network faults.

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