HP OpenVMS Systems Documentation

Depending on the level of network security required, you might also want to consider how other security mechanisms, such as protocol encryption and decryption, can promote additional security protection across the cluster.

Reference: See the HP OpenVMS Guide to System Security.

5.8 Coordinating System Files

Follow these guidelines to coordinate system files:

5.8.1 Procedure

To prepare a common user environment for an OpenVMS Cluster system that includes more than one common OpenVMS Integrity server system disk or more than one common OpenVMS Alpha system disk, you must coordinate the system files on those disks.

Rules: The following rules apply to the procedures described in Table 5-4:

• Disks holding common resources must be mounted early in the system startup procedure, such as in the SYLOGICALS.COM procedure.
• You must ensure that the disks are mounted with each OpenVMS Cluster reboot.

$ DEFINE/SYSTEM/EXEC SYSUAF -

 $1$DGA16:[VMS$COMMON.SYSEXE]SYSUAF.DAT

$ DEFINE/SYSTEM/EXEC NETPROXY -

 $1$DGA16:[VMS$COMMON.SYSEXE]NETPROXY.DAT

$ DEFINE/SYSTEM/EXEC RIGHTSLIST -

 $1$DGA16:[VMS$COMMON.SYSEXE]RIGHTSLIST.DAT

$ DEFINE/SYSTEM/EXEC VMSMAIL_PROFILE -

 $1$DGA16:[VMS$COMMON.SYSEXE]VMSMAIL_PROFILE.DATA

$ DEFINE/SYSTEM/EXEC NETNODE_REMOTE -

 $1$DGA16:[VMS$COMMON.SYSEXE]NETNODE_REMOTE.DAT

$ DEFINE/SYSTEM/EXEC NETNODE_UPDATE -

 $1$DGA16:[VMS$COMMON.SYSMGR]NETNODE_UPDATE.COM

$ DEFINE/SYSTEM/EXEC QMAN$MASTER -

 $1$DGA16:[VMS$COMMON.SYSEXE]

$ @SYS$SYSDEVICE:[VMS$COMMON.SYSMGR]CLU_MOUNT_DISK.COM $1$DGA16:
volume-label

$ START/QUEUE/MANAGER $1$DGA16:[VMS$COMMON.SYSEXE]

In OpenVMS Cluster systems on the LAN and in mixed-interconnect clusters, you must also coordinate the SYS$MANAGER:NETNODE_UPDATE.COM file, which is a file that contains all essential network configuration data for satellites. NETNODE_UPDATE.COM is updated each time you add or remove a satellite or change its Ethernet or FDDI hardware address. This file is discussed more thoroughly in Section 10.4.2.

In OpenVMS Cluster systems configured with DECnet for OpenVMS software, you must also coordinate NETNODE_REMOTE.DAT, which is the remote node network database.

5.9 System Time on the Cluster

When a computer joins the cluster, the cluster attempts to set the joining computer's system time to the current time on the cluster. Although it is likely that the system time will be similar on each cluster computer, there is no assurance that the time will be set. Also, no attempt is made to ensure that the system times remain similar throughout the cluster. (For example, there is no protection against different computers having different clock rates.)

An OpenVMS Cluster system spanning multiple time zones must use a single, clusterwide common time on all nodes. Use of a common time ensures timestamp consistency (for example, between applications, file-system instances) across the OpenVMS Cluster members.

5.9.1 Setting System Time

Use the SYSMAN command CONFIGURATION SET TIME to set the time across the cluster. This command issues warnings if the time on all nodes cannot be set within certain limits. Refer to the HP OpenVMS System Manager's Manual for information about the SET TIME command.

One of the most important features of OpenVMS Cluster systems is the ability to provide access to devices and files across multiple systems.

In a traditional computing environment, a single system is directly attached to its storage subsystems. Even though the system may be networked with other systems, when the system is shut down, no other system on the network has access to its disks or any other devices attached to the system.

In an OpenVMS Cluster system, disks and tapes can be made accessible to one or more members. So, if one computer shuts down, the remaining computers still have access to the devices.

6.1 Data File Sharing

Cluster-accessible devices play a key role in OpenVMS Clusters because, when you place data files or applications on a cluster-accessible device, computers can share a single copy of each common file. Data sharing is possible between Integrity server systems, between:

• Integrity servers
• Integrity servers and AlphaServer systems
• AlphaServer systems

In addition, multiple systems that are permitted in the same OpenVMS Cluster system can write to a shared disk file simultaneously. It is this ability that allows multiple systems in an OpenVMS Cluster to share a single system disk; multiple systems can boot from the same system disk and share operating system files and utilities to save disk space and simplify system management.

Note: Tapes do not allow multiple systems to access a tape file simultaneously.

6.1.1 Access Methods

Depending on your business needs, you may want to restrict access to a particular device to the users on the computer that are directly connected (local) to the device. Alternatively, you may decide to set up a disk or tape as a served device so that any user on any OpenVMS Cluster computer can allocate and use it.

Table 6-1 describes the various access methods.

When storage subsystems are connected directly to a specific system, the availability of the subsystem is lower due to the reliance on the host system. To increase the availability of these configurations, OpenVMS Cluster systems support dual porting, dual pathing, and MSCP and TMSCP serving.

Figure 6-1 shows a dual-ported configuration, in which the disks have independent connections to two separate computers. As long as one of the computers is available, the disk is accessible by the other systems in the cluster.

Figure 6-1 Dual-Ported Disks

Note: Disks can be shadowed using Volume Shadowing for OpenVMS. The automatic recovery from system failure provided by dual porting and shadowing is transparent to users and does not require any operator intervention.

Figure 6-2 shows a dual-pathed FC and Ethernet configuration. The disk devices, accessible through a shared SCSI interconnect, are MSCP served to the client nodes on the LAN.

Rule: A dual-pathed DSA disk cannot be used as a system disk for a directly connected CPU. Because a device can be on line to one controller at a time, only one of the server nodes can use its local connection to the device. The second server node accesses the device through the MSCP (or the TMSCP server). If the computer that is currently serving the device fails, the other computer detects the failure and fails the device over to its local connection. The device thereby remains available to the cluster.

Figure 6-2 Dual-Pathed Disks

Dual-pathed disks or tapes can be failed over between two computers that serve the devices to the cluster, provided that:

• The same device controller letter is generated and the same allocation class is specified on each computer, with the result that the device has the same name on both systems. ( Section 6.2.1 describes allocation classes.)
• Both computers are running the MSCP server for disks, the TMSCP server for tapes, or both.

Caution: Failure to observe these requirements can endanger data integrity.

You can set up HSG or HSV storage devices to be dual ported between two storage subsystems, as shown in Figure 6-3.

Figure 6-3 Configuration with Cluster-Accessible Devices

By design, HSG and HSV disks and tapes are directly accessible by all OpenVMS Cluster nodes that are connected to the same star coupler. Therefore, if the devices are dual ported, they are automatically dual pathed. Computers connected by FC can access a dual-ported HSG or HSV device by way of a path through either subsystem connected to the device. If one subsystem fails, access fails over to the other subsystem.

Note: To control the path that is taken during failover, you can specify a preferred path to force access to disks over a specific path. Section 6.1.3 describes the preferred-path capability.

See Chapter 6 of Guidelines for OpenVMS Cluster Configurations, Configuring Multiple Paths to SCSI and Fibre Channel Storage for more information on FC storage devices.

6.1.3 Specifying a Preferred Path

The operating system supports specifying a preferred path for DSA disks, including RA series disks and disks that are accessed through the MSCP server. (This function is not available for tapes.) If a preferred path is specified for a disk, the MSCP disk class drivers use that path:

• For the first attempt to locate the disk and bring it on line with a DCL command MOUNT
• For failover of an already mounted disk

In addition, you can initiate failover of a mounted disk to force the disk to the preferred path or to use load-balancing information for disks accessed by MSCP servers.

You can specify the preferred path by using the SET PREFERRED_PATH DCL command or by using the $QIO function (IO$_SETPRFPATH), with the P1 parameter containing the address of a counted ASCII string (.ASCIC). This string is the node name of the HSG or HSV, or of the OpenVMS system that is to be the preferred path.

Rule: The node name must match an existing node running the MSCP server that is known to the local node.

Reference: For more information about the use of the SET PREFERRED_PATH DCL command, refer to the HP OpenVMS DCL Dictionary: N--Z.

For more information about the use of the IO$_SETPRFPATH function, refer to the HP OpenVMS I/O User's Reference Manual.

6.2 Naming OpenVMS Cluster Storage Devices

In the OpenVMS operating system, a device name takes the form of ddcu, where:

• dd represents the predefined code for the device type
• c represents the predefined controller designation
• u represents the unit number

For SCSI, the controller letter is assigned by OpenVMS, based on the system configuration. The unit number is determined by the SCSI bus ID and the logical unit number (LUN) of the device.

Because device names must be unique in an OpenVMS Cluster, and because every cluster member must use the same name for the same device, OpenVMS adds a prefix to the device name, as follows:

• If a device is attached to a single computer, the device name is extended to include the name of that computer:

  node$ddcu

  
  where node represents the SCS node name of the system on which the device resides.
• If a device is attached to multiple computers, the node name part of the device name is replaced by a dollar sign and a number (called a node or port allocation class, depending on usage), as follows:

  $allocation-class$ddcu

• SAS disks follow the device naming similar to that of SCSI devices, that is, Target-LUN numbering. So a disk on SAS target ID 1 and LUN 0 will be named as DKA100. For SAS tapes you can use the Fibre channel naming convention, that is, DGAtxx: The SYSGEN parameter SAS_NAMING can be used to use SCSI numbering in tapes also.

The purpose of allocation classes is to provide unique and unchanging device names. The device name is used by the OpenVMS Cluster distributed lock manager in conjunction with OpenVMS facilities (such as RMS and the XQP) to uniquely identify shared devices, files, and data.

Allocation classes are required in OpenVMS Cluster configurations where storage devices are accessible through multiple paths. Without the use of allocation classes, device names that relied on node names would change as access paths to the devices change.

Prior to OpenVMS Version 7.1, only one type of allocation class existed, which was node based. It was named allocation class. OpenVMS Version 7.1 introduced a second type, port allocation class, which is specific to a single interconnect and is assigned to all devices attached to that interconnect. Port allocation classes were originally designed for naming SCSI devices. Their use has been expanded to include additional devices types: floppy disks, PCI RAID controller disks, and IDE disks.

The use of port allocation classes is optional. They are designed to solve the device-naming and configuration conflicts that can occur in certain configurations, as described in Section 6.2.3.

To differentiate between the earlier node-based allocation class and the newer port allocation class, the term node allocation class was assigned to the earlier type.

Prior to OpenVMS Version 7.2, all nodes with direct access to the same multipathed device were required to use the same nonzero value for the node allocation class. OpenVMS Version 7.2 introduced the MSCP_SERVE_ALL system parameter, which can be set to serve all disks or to exclude those whose node allocation class differs.

Multipathed MSCP controllers also have an allocation class parameter, which is set to match that of the connected nodes. (If the allocation class does not match, the devices attached to the nodes cannot be served.)

6.2.2 Specifying Node Allocation Classes

A node allocation class can be assigned to computers, HSG or HSV controllers. The node allocation class is a numeric value from 1 to 255 that is assigned by the system manager.

The default node allocation class value is 0. A node allocation class value of 0 is appropriate only when serving a local, single-pathed disk. If a node allocation class of 0 is assigned, served devices are named using the node-name$device-name syntax, that is, the device name prefix reverts to the node name.

The following rules apply to specifying node allocation class values:

1. When serving satellites, the same nonzero node allocation class value must be assigned to the serving computers and controllers.
2. All cluster-accessible devices on computers with a nonzero node allocation class value must have unique names throughout the cluster. For example, if two computers have the same node allocation class value, it is invalid for both computers to have a local disk named DGA0 or a tape named MUA0. This also applies to HSG and HSV subsystems.

System managers provide node allocation classes separately for disks and tapes. The node allocation class for disks and the node allocation class for tapes can be different.

The node allocation class names are constructed as follows:

$disk-allocation-class$device-name
$tape-allocation-class$device-name

Caution: Failure to set node allocation class values and device unit numbers correctly can endanger data integrity and cause locking conflicts that suspend normal cluster operations.

Figure 6-5 includes satellite nodes that access devices $1$DUA17 and $1$MUA12 through the JUPITR and NEPTUN computers. In this configuration, the computers JUPITR and NEPTUN require node allocation classes so that the satellite nodes are able to use consistent device names regardless of the access path to the devices.

Note: System management is usually simplified by using the same node allocation class value for all servers, HSG and HSV subsystems; you can arbitrarily choose a number between 1 and 255. Note, however, that to change a node allocation class value, you must shut down and reboot the entire cluster (described in Section 8.6). If you use a common node allocation class for computers and controllers, ensure that all devices have unique unit numbers.