Glossary

The terms in this glossary are commonly used in a TruCluster Server environment.

Click letter for quick access: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

A

action script

Shell scripts used by CAA to control how applications are started, stopped, and checked. By default, action scripts are located in the /var/cluster/caa/script directory. The file names of action scripts take the form resource_name.scr.

adapter

A device that converts the protocol and hardware interface of one bus type into that of another bus.

address switches

Electrical switches on some disk drives that determine the SCSI address setting for the drive.

alias router

A cluster member that makes a cluster alias address known to the network and receives incoming packets for that alias. By default, all cluster members are configured as alias routers at boot time.

availability

The characteristic of a computing system that allows it to provide computing services (such as applications) to clients with little or no disruption.

See also highly available

B

bus

Flat or twisted-wire cable or a backplane composed of individual parallel circuits. A bus connects computer system components to provide communications paths for addresses, data, and control information.

C

CAA

cluster application availability. A subsystem that provides high availability for single-instance applications and monitoring of the state of other types of resources (such as network interfaces). A single instance of any application that can run on Tru64 UNIX can be made highly available in a cluster with CAA.

CDSL

context-dependent symbolic link. A special form of a symbolic link whose target pathname includes an environment variable, such as {memb}, which is resolved at run time. In a cluster, CDSLs make it possible to maintain per-system configuration and data files within the shared CFS root (/), /usr, and /var file systems.

CFS

Cluster File System. A virtual file system that sits above the physical file systems and provides clusterwide access (with assistance from the device request dispatcher) to all mounted file systems in a cluster. CFS maintains cache coherency across all cluster members, which ensures that all members have an identical, consistent view of file systems directly connected to the cluster.

client

A computer system that uses resources provided by another computer, called a server.

cluster

A loosely coupled collection of servers that share storage and other resources that make applications and data highly available. A cluster consists of communications media, member systems, peripheral devices, and applications. The systems communicate over a cluster interconnect.

cluster alias

An IP address that is used to address all or a subset of the members in a cluster. A cluster alias makes some or all of the systems in a cluster look like a single system to the outside world.

cluster application availability (CAA)

See CAA

cluster expected votes

See expected votes

Cluster File System (CFS)

See CFS

cluster interconnect

A private interconnect that cluster members use for intracluster communication.

cluster member

The basic computing resource in a cluster. A member system must be physically connected to a cluster interconnect.

In common usage, a system configured with TruCluster Server software that is capable of forming or joining a cluster. From the point of view of the connection manager, a system that has either formed a single-member cluster or has been granted membership in an existing cluster. The connection manager dynamically determines cluster membership based on communications among the cluster members. Only an active cluster member can access the shared resources of a cluster.

cluster partition

An abnormal condition in which nodes in an existing cluster divide into multiple independent clusters.

common subnet

In the context of cluster aliases, an existing physical subnet. Cluster alias IP addresses are either in a common subnet or in a virtual subnet.

connection manager

The cluster software component that coordinates participation of systems in the cluster, and maintains cluster integrity when systems join or leave the cluster.

context-dependent symbolic link (CDSL)

See CDSL

current votes

The number of votes contributed by current cluster members and by the quorum disk as seen by this member.

dedicated port

See locked port

default cluster alias

A special cluster alias created during cluster installation. All cluster members are, by default, members of the default cluster alias.

device request dispatcher

A kernel subsystem that controls all I/O access to storage devices in a cluster. The device request dispatcher supports clusterwide access to both character and block disk devices.

Note: Do not confuse the device request dispatcher with the Distributed Raw Disk (DRD) services provided in the TruCluster Production Server product. The device request dispatcher is fully integrated with the kernel, and removes the need for having a specific service to make storage accessible to cluster members.

differential SCSI bus

A SCSI bus where the signal's level is determined by the voltage differential between two wires.

direct-access cached reads

A performance enhancement for AdvFS file systems. Direct-access cached reads allow CFS to read directly from storage simultaneously on behalf of multiple cluster members.

direct-access I/O device

An I/O device that supports simultaneous access from multiple cluster members.

See also single-server device

distributed application

An application that is specifically designed to run on a cluster, using different members for specific purposes. These applications use the Memory Channel, distributed lock manager (DLM), and cluster alias application programming interfaces to integrate application with the cluster resources.

distributed lock manager (DLM)

See DLM

DLM

distributed lock manager. A software component that synchronizes access to shared resources among cooperating processes throughout the cluster.

Event Manager (EVM)

See EVM

EVM

Event Manager. A facility that lets kernel-level and user-level processes and components post events, and provides a means for processes to subscribe for notification when selected events occur. The facility provides an event viewer, an API, and command-line utilities. See EVM(5) for more information.

expected votes

The sum of all node votes held by cluster members, plus the vote of the quorum disk, if one is defined.

F

failover

A transfer of the responsibility to provide services. A failover occurs when a hardware or software failure causes a service to restart on another member system.

failover pair

A Memory Channel logical rail configuration that consists of two physical rails, with one physical rail active and the other inactive. If the active physical rail fails, a failover takes place and the inactive physical rail is used.

fast SCSI

An optional mode of SCSI-2 that allows transmission rates of up to 10 MB per second.

file system partitioning

Mounting an AdvFS file system so that it is accessible to only a single cluster member.

File system partitioning is provided to ease migration from TruCluster Production Server Software or TruCluster Available Server Software Version 1.5 or Version 1.6. File system partitioning is not intended as a general purpose method for restricting file system access to a single member.

H

highly available

In the TruCluster Server software, the ability to survive any single hardware or software failure.

A cluster can be considered highly available if the hardware and software provide protection against any single failure, such as a system failure, disk failure, or a SCSI cable disconnection.

A service can be considered highly available if the hardware that it depends on provides protection against any single failure, and the service is configured to fail over in case of a failure.

host route

When discussing routing for cluster aliases, an advertised route (using RIP) to a cluster alias IP address via a local IP address on a cluster node, using a subnet mask of all 1s.

hot swap

The ability to replace a device on a shared bus while the bus is active.

I

in_multi service

A designation on a service port that causes the cluster alias subsystem to route connection requests and packets to all eligible members of the alias.

in_noalias service

A designation on a service port that causes the cluster alias subsystem to ensure that the port will not receive inbound alias messages.

in_nolocal service

A designation on a service port that causes the cluster alias subsystem to ensure that the port will not honor connection requests to a nonalias address.

in_single service

A designation on a service port that causes the cluster alias subsystem to ensure that only one alias member will receive connection requests or packets for that service.

local bus

See private bus

lock file

A file that indicates that operations on one or more other files are restricted or prohibited. The presence of the lock file can be used as the indication, or the lock file can contain information describing the nature of the restrictions.

locked port

A port in the clusterwide port space that is dedicated for use by a single node in the cluster.

logical rail

One or more Memory Channel physical rails. Logical rails are configured as a single-rail or as a failover pair.

Logical Storage Manager (LSM)

See LSM

logical unit number (LUN)

See LUN

LSM

Logical Storage Manager. A disk storage management tool that protects against data loss, improves disk I/O performance, and customizes the disk configuration.

System administrators use LSM to perform disk management functions without disrupting users or applications accessing data on those disks.

LSM disk group

A group of Logical Storage Manager (LSM) disks that share a common configuration. The configuration information for an LSM disk group consists of a set of records describing objects including LSM disks, LSM volumes, LSM plexes, and LSM subdisks that are associated with the LSM disk group. Each LSM disk group has an administrator-assigned name that can be used to reference that LSM disk group.

LSM plex

A copy of an LSM volume's logical data address space, which is sometimes known as a mirror. An LSM volume can have up to eight LSM plexes associated with it. A read can be satisfied from any LSM plex, while a write is directed to all LSM plexes.

LSM volume

A special device that contains data used by a UNIX file system, a database, or other applications. LSM transparently places an LSM volume between applications and a physical disk. Applications then operate on the LSM volume rather than on the physical disk. For example, a file system is created on an LSM volume rather than on a physical disk.

An LSM volume presents block and raw interfaces that are compatible in their use with disk partition special devices. Because an LSM volume is a virtual device, it can be mirrored, spanned across disk drives, moved to use different storage, and striped using administrative commands. The configuration of an LSM volume can be changed using LSM utilities without disrupting applications or file systems that are using the LSM volume.

LUN

logical unit number. A physical or virtual peripheral device addressable through a target. LUNs use their target's bus connection to communicate on a SCSI bus.

member

See cluster member

member ID

An integer, in the range 1-63, that identifies a cluster member system. Each member has a unique member ID, which is assigned during the installation procedure.

Memory Channel interconnect

A peripheral component interconnect (PCI) cluster interconnect that provides fast and reliable communications between cluster members. Physically, the interconnect consists of a Memory Channel adapter installed in a PCI slot in each member system, one or more Memory Channel link cables to connect the adapters, and an optional Memory Channel hub.

multi-instance application

An application that can run on multiple cluster members at the same time. A multi-instance application is, by definition, highly available because the failure of one cluster member does not affect the instances of the application running on other members.

N

network route

When discussing routing for cluster aliases, an advertised route (using RIP) to a virtual subnet in which one or more cluster alias IP addresses reside.

node votes

The fixed number of votes that a given member contributes toward quorum.

nonvoting member

A cluster member with 0 (zero) votes.

See also voting member

O

out_alias service

A designation on a service port that causes the cluster alias subsystem to ensure that the default cluster alias is used as the source address whenever the port is used as a destination.

P

PCI

peripheral component interconnect. An industry-standard expansion I/O bus that is a synchronous, asymmetrical I/O channel.

peripheral component interconnect (PCI)

See PCI

personality module

The module on a storage shelf that provides the interface between a differential SCSI bus and the storage shelf single-ended SCSI bus. Switches on the module enable SCSI bus termination and control SCSI bus IDs for the storage shelf.

physical rail

A Memory Channel hub with its cables and Memory Channel adapters and the Memory Channel driver for the adapters on each node.

See also logical rail

placement policy

A policy that determines where an application under CAA control runs. Supported policies are: balanced, favored, and restricted.

private bus

A bus that connects private storage to the local system.

private storage

A storage device on a private bus. Storage devices include hard disks, floppy disks, tape drives, and other devices.

proxy ARP

The mechanism that cluster members use to handle requests that are addressed to cluster aliases whose addresses reside on common subnets. The Address Resolution Protocol (ARP) maps dynamically between IP addresses and Ethernet addresses. An ARP request contains the IP address of an interface on the target host. The host that recognizes this IP address should respond with its Ethernet address. All other hosts should ignore the ARP request.

Proxy ARP is, in essence, when a system or router lies about being the system with an interface that matches the IP address in the ARP request. The proxy ARP system responds to the ARP request by returning its own Ethernet address. The system then routes the packets to the real target system. Proxy ARP is useful for subnetting and also when adding routers to a topology where some hosts are not yet configured to use the routers.

The cluster member that is acting as the proxy ARP master for an alias responds to an ARP request for a cluster alias IP address using one of its own network interfaces.

Q

quorum

A cluster state in which members are allowed to access clusterwide shared resources and thus perform useful work. The cluster has quorum when the connection manager determines that the sum of the node votes and quorum disk votes in the cluster equals or exceeds the required number of quorum votes.

See also quorum votes

quorum algorithm

A mathematical method that the connection manager uses to determine the circumstances under which a given member can participate in a cluster, safely accessing clusterwide resources and performing useful work.

quorum disk

A disk whose h partition contains cluster status and quorum information. Each cluster can have a maximum of one quorum disk. The quorum disk is assigned votes that are used when calculating quorum.

quorum disk votes

The number of votes that a quorum disk contributes towards quorum.

quorum loss

A cluster state in which no member is allowed to access clusterwide shared resources. A cluster enters a quorum loss state when the connection manager determines that the member and quorum disk votes in the cluster are less than the required number of quorum votes.

See also quorum votes

quorum votes

The number of votes that are required to form or maintain a cluster. The formula for calculating quorum votes is:

quorum votes = round_down((cluster-expected-votes+2)/2)

R

RAID

Redundant array of independent disks. A technique that organizes disk data to improve performance and reliability. RAID has three attributes:

• It is a set of physical disks that the user views as a single logical device or multiple logical devices.

• Disk data is distributed across the physical set of drives in a defined manner.

• Redundant disk capacity is added so data can be recovered if a drive fails.

redundant

A term to describe duplicate hardware that provides spare capacity that can be used when a component fails.

redundant array of independent disks (RAID)

See RAID

resource

A cluster hardware or software component that provides a service to end users or to other software components. Examples of resources are disks, tapes, file systems, network interfaces, and application software.

resource manager

All the CAA daemons running on cluster members. These daemons are independent but they communicate with each other, sharing information about the status of the resources.

The resource manager communicates with all the components of the CAA subsystem, as well as the connection manager and the Event Manager (EVM). The resource manager also uses the resource monitors to monitor the status of a particular type of resource.

resource monitor

A monitor that is loaded by the resource manager at boot time. There is one resource monitor for each type of resource (application, network, tape, and media changer).

resource profile

A file that contains an application's resource requirements. The file contains keyword/value pairs that are used by CAA to monitor resources and control application failover. Each application under CAA control has a resource profile. Resource profiles are located in the /var/cluster/caa/profile directory. The file names of resource profiles take the form resource_name.cap.

RIP

Routing Information Protocol. A protocol that is used to exchange routing information among gateways and other hosts. The protocol was defined in RFC 1058, and updated in RFCs 1388 and 1723.

rolling upgrade

A software upgrade of a cluster that is performed while the cluster is in operation. One member at a time is rolled and returned to operation while the cluster transparently maintains a mixed-version environment for the base operating system, cluster, and Worldwide Language Support (WLS) software. Clients accessing services are not aware that a rolling upgrade is in progress.

router priority

A method that controls the proxy ARP router selection for a cluster alias on a common subnet. For each alias in a common subnet, the cluster member with the highest router priority for that alias will route for that alias.

Routing Information Protocol (RIP)

See RIP

S

SCSI

Small Computer System Interface. A standard, maintained by the American National Standards Institute (ANSI), that provides a standard interface for connecting disks and other peripheral devices to a computer system. SCSI-based devices can be configured in a series, with multiple devices on the same bus.

SCSI-2

An extension to the original SCSI standard featuring multiple systems on the same bus and hot swap. The SCSI-2 standard is ANSI standard X3.T9.2/86-109.

SCSI adapter

A storage adapter, commonly referred to as a host bus adapter (HBA), that provides a connection between an I/O bus and a SCSI bus.

SCSI bus

A bus that supports the transmission and signaling requirements of a SCSI protocol.

SCSI bus speed

The data transfer speed for a SCSI bus. SCSI bus speed can be slow, up to 5 MB/s; fast, up to 10 MB/s; fast and wide, up to 20 MB/s; or UltraSCSI, up to 40 MB/s.

SCSI controller

See SCSI adapter

SCSI device

A SCSI adapter, peripheral controller, or intelligent peripheral that can be attached to a SCSI bus.

SCSI ID

A unique address, from 0 through 15, that identifies a device on a SCSI bus.

selection priority

A priority assigned to a cluster alias that determines the order in which members of the alias receive new connection requests. The selection priority establishes a hierarchy within the members of an alias. Connection requests are distributed among those members sharing the highest selection priority value.

selection weight

The number of connections (on average) a member is given before connections are given to the next alias member with the same selection priority value.

shared bus

A bus that is connected to more than one member system and, optionally, to one or more storage devices.

shared storage

Disks that are connected to a shared bus.

signal converter

A device that converts signals between a single-ended SCSI bus and a differential SCSI bus.

single-ended SCSI bus

A signal path in which one data lead and one ground lead are utilized to make a device connection. This transmission method is economical, but is more susceptible to noise than a differential SCSI bus.

single-instance application

An application that is run on only one cluster member at a time. The cluster application availability (CAA) subsystem can provide high availability for single-instance applications by controlling their initial startup and failover characteristics.

single rail

A Memory Channel logical rail configuration where there is a one-to-one relationship between physical rails and logical rails. This configuration has no failover properties; if the physical rail fails, the logical rail fails.

single-server device

A device that supports access from only a single member.

See also direct-access I/O device

Small Computer System Interface (SCSI)

See SCSI

SRM

The external interface to console firmware for operating systems that expect firmware compliance with the Alpha System Reference Manual (SRM).

standard hub mode

A Memory Channel interconnect configuration that uses a Memory Channel hub to connect Memory Channel adapters. To set up a Memory Channel interconnect in standard mode, use a link cable to connect each Memory Channel adapter to a linecard installed in a Memory Channel hub.

static service

A designation on a service port that causes the cluster alias subsystem to ensure that the port will not be assigned as a dynamic port.

subset

An installable software module that is compatible with the Tru64 UNIX setld software installation utility.

tunneling

In the context of cluster aliases, moving an mbuf chain between cluster members after receipt.

U

UltraSCSI

A differential SCSI bus standard that uses smaller diameter cables with smaller connectors and allows bus speeds up to 40 MB/s at 25 meters (approximately 82 feet).

UltraSCSI hub

A specialized signal converter with multiple connectors. An UltraSCSI hub converts differential input SCSI signals from a host bus adapter to single-ended, then converts the single-ended signals back to differential for the output connection to a RAID array controller. An UltraSCSI hub allows radial connection of UltraSCSI devices and increases the separation between host and storage.

V

virtual hub mode

A Memory Channel interconnect configuration that does not use a Memory Channel hub to connect Memory Channel adapters. Virtual hub mode is supported only for clusters that have two member systems. To set up a Memory Channel interconnect in virtual hub mode, use a Memory Channel link cable to connect the Memory Channel adapter in one member system to the corresponding Memory Channel adapter in the other member system.

virtual subnet

In the context of cluster aliases, a subnet with no physical connections. Cluster alias IP addresses are either in a common subnet or in a virtual subnet.

vMAC

In the context of cluster aliases, a unique hardware address that can be automatically created for each alias IP address. An alias vMAC (virtual Media Access Control) address follows the cluster alias proxy ARP master from node to node as needed. Regardless of which cluster member is serving as the proxy ARP master for an alias, the alias's vMAC address does not change.

votes

See quorum

voting member

A cluster member with a vote.

See also nonvoting member

worldwide ID (WWID)

See WWID

WWID

Worldwide identifier. A unique ID that a manufacturer assigns to a disk.

Y

Y cable

A cable that joins two cables to a single device, or allows terminating a shared SCSI bus external to the adapter or RAID controller.