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Red Hat CLUSTER SUITE FOR ENTERPRISE LINUX 5.2, Overview

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Figure 1.13. GFS and GNBD with Directly Connected Storage

6. Cluster Logical Volume Manager

The Cluster Logical Volume Manager (CLVM) provides a cluster-wide version of LVM2. CLVM

provides the same capabilities as LVM2 on a single node, but makes the volumes available to

all nodes in a Red Hat cluster. The logical volumes created with CLVM make logical volumes

available to all nodes in a cluster.

The key component in CLVM is

clvmd

.

clvmd

is a daemon that provides clustering extensions

to the standard LVM2 tool set and allows LVM2 commands to manage shared storage.

clvmd

runs in each cluster node and distributes LVM metadata updates in a cluster, thereby

presenting each cluster node with the same view of the logical volumes (refer to

Figure 1.14,

“CLVM Overview”

). Logical volumes created with CLVM on shared storage are visible to all

nodes that have access to the shared storage. CLVM allows a user to configure logical volumes

on shared storage by locking access to physical storage while a logical volume is being

configured. CLVM uses the lock-management service provided by the cluster infrastructure

(refer to

Section 3, “Cluster Infrastructure”

).

Note

Chapter 1. Red Hat Cluster Suite Overview

20

Summary of Contents for CLUSTER SUITE FOR ENTERPRISE LINUX 5.2

Page 1: ...Red Hat Cluster Suite Overview Red Hat Cluster Suite for Red Hat Enterprise Linux 5 2 Cluster_Suite_Overview ISBN N A Publication date May 2008 ...

Page 2: ...Red Hat Cluster Suite Overview provides an overview of Red Hat Cluster Suite for Red Hat Enterprise Linux 5 2 Red Hat Cluster Suite Overview ...

Page 3: ... permission of the copyright holder Distribution of the work or derivative of the work in any standard paper book form for commercial purposes is prohibited unless prior permission is obtained from the copyright holder Red Hat and the Red Hat Shadow Man logo are registered trademarks of Red Hat Inc in the United States and other countries All other trademarks referenced herein are the property of ...

Page 4: ...Red Hat Cluster Suite Overview ...

Page 5: ... 3 Economy and Performance 19 6 Cluster Logical Volume Manager 20 7 Global Network Block Device 24 8 Linux Virtual Server 25 8 1 Two Tier LVS Topology 27 8 2 Three Tier LVS Topology 30 8 3 Routing Methods 32 8 4 Persistence and Firewall Marks 35 9 Cluster Administration Tools 36 9 1 Conga 36 9 2 Cluster Administration GUI 39 9 3 Command Line Administration Tools 42 10 Linux Virtual Server Administ...

Page 6: ...vi ...

Page 7: ...inux 5 refer to the following resources Configuring and Managing a Red Hat Cluster Provides information about installing configuring and managing Red Hat Cluster components LVM Administrator s Guide Configuration and Administration Provides a description of the Logical Volume Manager LVM including information on running LVM in a clustered environment Global File System Configuration and Administra...

Page 8: ...old Courier font represents text that you are to type such as service jonas start If you have to run a command as root the root prompt precedes the command gconftool 2 italic Courier font Italic Courier font represents a variable such as an installation directory install_dir bin bold font Bold font represents application programs and text found on a graphical interface When shown like this OK it i...

Page 9: ... you spot a typo or if you have thought of a way to make this document better we would love to hear from you Please submit a report in Bugzilla http bugzilla redhat com bugzilla against the component Documentation cluster Be sure to mention the document s identifier Cluster_Suite_Overview EN 5 2 2008 06 01 T15 23 By mentioning this document s identifier we know exactly which version of the guide y...

Page 10: ...x ...

Page 11: ...tion 8 Linux Virtual Server Section 9 Cluster Administration Tools Section 10 Linux Virtual Server Administration GUI 1 Cluster Basics A cluster is two or more computers called nodes or members that work together to perform a task There are four major types of clusters Storage High availability Load balancing High performance Storage clusters provide a consistent file system image across servers i...

Page 12: ...nts outside the cluster Red Hat Cluster Suite provides load balancing through LVS Linux Virtual Server High performance clusters use cluster nodes to perform concurrent calculations A high performance cluster allows applications to work in parallel therefore enhancing the performance of the applications High performance clusters are also referred to as computational clusters or grid computing Note...

Page 13: ...iple nodes to share storage at a block level as if the storage were connected locally to each cluster node Cluster Logical Volume Manager CLVM Provides volume management of cluster storage Note When you create or modify a CLVM volume for a clustered environment you must ensure that you are running the clvmd daemon For further information refer to Section 6 Cluster Logical Volume Manager Global Net...

Page 14: ...ure provides the basic functions for a group of computers called nodes or members to work together as a cluster Once a cluster is formed using the cluster infrastructure you can use other Red Hat Cluster Suite components to suit your clustering needs for example setting up a cluster for sharing files on a GFS file system or setting up service failover The cluster infrastructure performs the follow...

Page 15: ...thernet Optionally quorum can be determined by a combination of communicating messages via Ethernet and through a quorum disk For quorum via Ethernet quorum consists of 50 percent of the node votes plus 1 For quorum via quorum disk quorum consists of user specified conditions Note By default each node has one quorum vote Optionally you can configure each node to have more than one vote CMAN keeps ...

Page 16: ...uster s shared storage Fencing cuts off I O from shared storage thus ensuring data integrity The cluster infrastructure performs fencing through the fence daemon fenced When CMAN determines that a node has failed it communicates to other cluster infrastructure components that the node has failed fenced when notified of the failure fences the failed node Other cluster infrastructure components dete...

Page 17: ...ts storage to an inoperable node GNBD fencing A fencing method that disables an inoperable node s access to a GNBD server Other fencing Several other fencing methods that disable I O or power of an inoperable node including IBM Bladecenters PAP DRAC MC HP ILO IPMI IBM RSA II and others Figure 1 3 Power Fencing Example shows an example of power fencing In the example the fencing program in node A c...

Page 18: ...Figure 1 3 Power Fencing Example Chapter 1 Red Hat Cluster Suite Overview 8 ...

Page 19: ...then the fencing method for the node must specify at least two fencing devices one fencing device for each power supply refer to Figure 1 5 Fencing a Node with Dual Power Supplies Similarly if a node has multiple paths to Fibre Channel storage then the fencing method for the node must specify one fencing device for each path to Fibre Channel storage For example if a node has two paths to Fibre Cha...

Page 20: ...Figure 1 5 Fencing a Node with Dual Power Supplies Chapter 1 Red Hat Cluster Suite Overview 10 ...

Page 21: ...of the fencing methods specified in the cluster configuration file If a node fails it is fenced using the first fencing method specified in the cluster configuration file for that node If the first fencing method is not successful the next fencing method specified for that node is used If none of the fencing methods is successful then fencing starts again with the first fencing method specified an...

Page 22: ...in each cluster node is up to date For example if a cluster system administrator updates the configuration file in Node A CCS propagates the update from Node A to the other nodes in the cluster refer to Figure 1 7 CCS Overview Figure 1 7 CCS Overview Other cluster components for example CMAN access configuration information from the configuration file through CCS refer to Figure 1 7 CCS Overview C...

Page 23: ...ing method for that node Fence Device Displays fence devices in the cluster Parameters vary according to the type of fence device For example for a power controller used as a fence device the cluster configuration defines the name of the power controller its IP address login and password Managed Resources Displays resources required to create cluster services Managed resources includes the definit...

Page 24: ...t a time to maintain data integrity You can specify failover priority in a failover domain Specifying failover priority consists of assigning a priority level to each node in a failover domain The priority level determines the failover order determining which node that a cluster service should fail over to If you do not specify failover priority a cluster service can fail over to any node in its f...

Page 25: ...ion the failover domain is configured with a failover priority to fail over to node D before node A and to restrict failover to nodes only in that failover domain The cluster service comprises these cluster resources IP address resource IP address 10 10 10 201 An application resource named httpd content a web server application init script etc init d httpd specifying httpd A file system resource R...

Page 26: ...Failover would occur with no apparent interruption to the cluster clients The cluster service would be accessible from another cluster node via the same IP address as it was before failover 5 Red Hat GFS Red Hat GFS is a cluster file system that allows a cluster of nodes to simultaneously access a block device that is shared among the nodes GFS is a native file system that interfaces directly with...

Page 27: ...CLVM Cluster Logical Volume Manager Red Hat GFS provides data sharing among GFS nodes in a Red Hat cluster GFS provides a single consistent view of the file system name space across the GFS nodes in a Red Hat cluster GFS allows applications to install and run without much knowledge of the underlying storage infrastructure Also GFS provides features that are typically required in enterprise environ...

Page 28: ...SAN configuration in Figure 1 11 GFS with a SAN provides superior file performance for shared files and file systems Linux applications run directly on cluster nodes using GFS Without file protocols or storage servers to slow data access performance is similar to individual Linux servers with directly connected storage yet each GFS application node has Figure 1 11 GFS with a SAN 5 2 Performance Sc...

Page 29: ...y shared by network client applications File locking and sharing functions are handled by GFS for each network client Figure 1 12 GFS and GNBD with a SAN 5 3 Economy and Performance Figure 1 13 GFS and GNBD with Directly Connected Storage shows how Linux client applications can take advantage of an existing Ethernet topology to gain shared access to all block storage devices Client data files and ...

Page 30: ...ard LVM2 tool set and allows LVM2 commands to manage shared storage clvmd runs in each cluster node and distributes LVM metadata updates in a cluster thereby presenting each cluster node with the same view of the logical volumes refer to Figure 1 14 CLVM Overview Logical volumes created with CLVM on shared storage are visible to all nodes that have access to the shared storage CLVM allows a user t...

Page 31: ...le instance LVM on the shared disk as this may result in data corruption If you have any concerns please contact your Red Hat service representative Note Using CLVM requires minor changes to etc lvm lvm conf for cluster wide locking Figure 1 14 CLVM Overview You can configure CLVM using the same commands as LVM2 using the LVM graphical user interface refer to Figure 1 15 LVM Graphical User Interfa...

Page 32: ...Figure 1 17 Creating Logical Volumes shows the basic concept of creating logical volumes from Linux partitions and shows the commands used to create logical volumes Figure 1 15 LVM Graphical User Interface Chapter 1 Red Hat Cluster Suite Overview 22 ...

Page 33: ...Figure 1 16 Conga LVM Graphical User Interface Cluster Logical Volume Manager 23 ...

Page 34: ...e not necessary or are cost prohibitive GNBD consists of two major components a GNBD client and a GNBD server A GNBD client runs in a node with GFS and imports a block device exported by a GNBD server A GNBD server runs in another node and exports block level storage from its local storage either directly attached storage or SAN storage Refer to Figure 1 18 GNBD Overview Multiple GNBD clients can ...

Page 35: ...e LVS router and one that is a backup LVS router The active LVS router serves two roles To balance the load across the real servers To check the integrity of the services on each real server The backup LVS router monitors the active LVS router and takes over from it in case the active LVS router fails Figure 1 19 Components of a Running LVS Cluster provides an overview of the LVS components and th...

Page 36: ...r Each nanny process checks the state of one configured service on one real server and tells the lvs daemon if the service on that real server is malfunctioning If a malfunction is detected the lvs daemon instructs ipvsadm to remove that real server from the IPVS routing table If the backup LVS router does not receive a response from the active LVS router it initiates failover by calling send_arp ...

Page 37: ...nc command for data synchronization does not function optimally Therefore for real servers with a high amount of uploads database transactions or similar traffic a three tiered topology is more appropriate for data synchronization 8 1 Two Tier LVS Topology Figure 1 20 Two Tier LVS Topology shows a simple LVS configuration consisting of two tiers LVS routers and real servers The LVS router tier con...

Page 38: ...ence at that IP address also known as floating IP addresses VIP addresses may be aliased to the same device that connects the LVS router to the public network For instance if eth0 is connected to the Internet then multiple virtual servers can be aliased to eth0 1 Alternatively each virtual server can be associated with a separate device per service For example HTTP traffic can be handled on eth0 1...

Page 39: ...ewer active connections relative to their destination IPs This algorithm is for use in a proxy cache server cluster It routes the packets for an IP address to the server for that address unless that server is above its capacity and has a server in its half load in which case it assigns the IP address to the least loaded real server Locality Based Least Connection Scheduling with Replication Schedu...

Page 40: ...kets addressed to the failed node When the failed node returns to active service the backup LVS router assumes its backup role again The simple two tier configuration in Figure 1 20 Two Tier LVS Topology is suited best for clusters serving data that does not change very frequently such as static web pages because the individual real servers do not automatically synchronize data among themselves 8 ...

Page 41: ...ored on a central highly available server and accessed by each real server via an exported NFS directory or Samba share This topology is also recommended for websites that access a central high availability database for transactions Additionally using an active active configuration with Three Tier LVS Topology 31 ...

Page 42: ...strates LVS using NAT routing to move requests between the Internet and a private network Figure 1 22 LVS Implemented with NAT Routing In the example there are two NICs in the active LVS router The NIC for the Internet has a real IP address on eth0 and has a floating IP address aliased to eth0 1 The NIC for the private network interface has a real IP address on eth1 and has a floating IP address a...

Page 43: ...router The LVS router uses network address translation to replace the address of the real server in the packets with the LVS routers public VIP address This process is called IP masquerading because the actual IP addresses of the real servers is hidden from the requesting clients Using NAT routing the real servers can be any kind of computers running a variety operating systems The main disadvanta...

Page 44: ...irectly to clients bypassing the LVS routers Direct routing allows for scalability in that real servers can be added without the added burden on the LVS router to route outgoing packets from the real server to the client which can become a bottleneck under heavy network load While there are many advantages to using direct routing in LVS there are limitations The most common issue with direct routi...

Page 45: ...sociate the VIP to the LVS router which will properly process the requests and send them to the real server pool This can be done by using the arptables packet filtering tool 8 4 Persistence and Firewall Marks In certain situations it may be desirable for a client to reconnect repeatedly to the same real server rather than have an LVS load balancing algorithm send that request to the best availabl...

Page 46: ...ls Red Hat Cluster Suite provides a variety of tools to configure and manage your Red Hat Cluster This section provides an overview of the administration tools available with Red Hat Cluster Suite Section 9 1 Conga Section 9 2 Cluster Administration GUI Section 9 3 Command Line Administration Tools 9 1 Conga Conga is an integrated set of software components that provides centralized configuration ...

Page 47: ...nstance That capability provides a means of replicating a luci server instance and provides an efficient upgrade and testing path When you install an instance of luci its database is empty However you can import part or all of a luci database from an existing luci server when deploying a new luci server Each luci instance has one user at initial installation admin Only the admin user may add syste...

Page 48: ...Figure 1 24 luci homebase Tab Figure 1 25 luci cluster Tab Chapter 1 Red Hat Cluster Suite Overview 38 ...

Page 49: ...r Infrastructure and Section 4 High availability Service Management The GUI consists of two major functions the Cluster Configuration Tool and the Cluster Status Tool The Cluster Configuration Tool provides the capability to create edit and propagate the cluster configuration file etc cluster cluster conf The Cluster Status Tool provides the capability to manage high availability services The foll...

Page 50: ...ts cluster configuration components in the configuration file etc cluster cluster conf with a hierarchical graphical display in the left panel A triangle icon to the left of a component name indicates that the component has one or more subordinate components assigned to it Clicking the triangle icon expands and collapses the portion of the tree below a component The components displayed in the GUI...

Page 51: ...main is selected Resources For configuring shared resources to be used by high availability services Shared resources consist of file systems IP addresses NFS mounts and exports and user created scripts that are available to any high availability service in the cluster Resources are represented as subordinate elements under Resources Using configuration buttons at the bottom of the right frame bel...

Page 52: ... the Cluster Status Tool to enable disable restart or relocate a high availability service 9 3 Command Line Administration Tools In addition to Conga and the system config cluster Cluster Administration GUI command line tools are available for administering the cluster infrastructure and the high availability service management components The command line tools are used by the Cluster Chapter 1 Re...

Page 53: ...or more information about this tool refer to the fence_tool 8 man page clustat Cluster Status Utility High availability Service Management Components The clustat command displays the status of the cluster It shows membership information quorum view and the state of all configured user services For more information about this tool refer to the clustat 8 man page clusvcadm Cluster User Service Admin...

Page 54: ...o the welcome page provides access to the four main screens or panels CONTROL MONITORING GLOBAL SETTINGS REDUNDANCY and VIRTUAL SERVERS In addition the VIRTUAL SERVERS panel contains four subsections The CONTROL MONITORING panel is the first panel displayed after you log in at the welcome screen Figure 1 29 The Welcome Panel The following sections provide a brief description of the Piranha Configu...

Page 55: ...erval less than 10 seconds Doing so may make it difficult to reconfigure the Auto update interval because the page will update too frequently If you encounter this issue simply click on another panel and then back on CONTROL MONITORING Update information now Provides manual update of the status information CHANGE PASSWORD Clicking this button takes you to a help screen with information on how to c...

Page 56: ...l sets up the primary LVS router s public and private network interfaces Primary server public IP The publicly routable real IP address for the primary LVS node Primary server private IP The real IP address for an alternative network interface on the primary LVS node This address is used solely as an alternative heartbeat channel for the backup router Use network type Selects select NAT routing Ch...

Page 57: ...ould be used as the gateway for the real servers NAT Router netmask If the NAT router s floating IP needs a particular netmask select it from drop down list NAT Router device Defines the device name of the network interface for the floating IP address such as eth1 1 10 3 REDUNDANCY The REDUNDANCY panel allows you to configure of the backup LVS router node and set various heartbeat monitoring optio...

Page 58: ... dead after seconds If the primary LVS node does not respond after this number of seconds then the backup LVS router node will initiate failover Heartbeat runs on port Sets the port at which the heartbeat communicates with the primary LVS node The default is set to 539 if this field is left blank 10 4 VIRTUAL SERVERS The VIRTUAL SERVERS panel displays information for each currently defined virtual...

Page 59: ...ble click its radio button and click the DE ACTIVATE button After adding a virtual server you can configure it by clicking the radio button to its left and clicking the EDIT button to display the VIRTUAL SERVER subsection 10 4 1 The VIRTUAL SERVER Subsection The VIRTUAL SERVER subsection panel shown in Figure 1 34 The VIRTUAL SERVERS Subsection allows you to configure an individual virtual server ...

Page 60: ...ame is not the hostname for the machine so make it descriptive and easily identifiable You can even reference the protocol used by the virtual server such as HTTP Application port The port number through which the service application will listen Protocol Provides a choice of UDP or TCP in a drop down menu Virtual IP Address The virtual server s floating IP address Chapter 1 Red Hat Cluster Suite O...

Page 61: ...me a new real server node comes online the least connections table is reset to zero so the active LVS router routes requests as if all the real servers were freshly added to the cluster This option prevents the a new server from becoming bogged down with a high number of connections upon entering the cluster Load monitoring tool The LVS router can monitor the load on the various real servers by us...

Page 62: ...physical server hosts for a particular virtual service Figure 1 35 The REAL SERVER Subsection Click the ADD button to add a new server To delete an existing server select the radio button beside it and click the DELETE button Click the EDIT button to load the EDIT REAL SERVER panel as seen in Figure 1 36 The REAL SERVER Configuration Panel Chapter 1 Red Hat Cluster Suite Overview 52 ...

Page 63: ...A descriptive name for the real server Tip This name is not the hostname for the machine so make it descriptive and easily identifiable Address The real server s IP address Since the listening port is already specified for the associated virtual server do not add a port number VIRTUAL SERVERS 53 ...

Page 64: ...trator to specify a send expect string sequence to verify that the service for the virtual server is functional on each real server It is also the place where the administrator can specify customized scripts to check services requiring dynamically changing data Figure 1 37 The EDIT MONITORING SCRIPTS Subsection Sending Program For more advanced service verification you can use this field to specif...

Page 65: ...d for HTTP You can alter this value depending on your needs If you leave this field blank the nanny daemon attempts to open the port and assume the service is running if it succeeds Only one send sequence is allowed in this field and it can only contain printable ASCII characters as well as the following escape characters n for new line r for carriage return t for tab to escape the next character ...

Page 66: ...56 ...

Page 67: ...d used to manage cluster configuration in a graphical setting Cluster Logical Volume Manager CLVM clvmd The daemon that distributes LVM metadata updates around a cluster It must be running on all nodes in the cluster and will give an error if a node in the cluster does not have this daemon running lvm LVM2 tools Provides the command line tools for LVM2 system config lvm Provides graphical user int...

Page 68: ...ernal parameters such as votes dlm_controld Daemon started by cman init script to manage dlm in kernel not used by user gfs_controld Daemon started by cman init script to manage gfs in kernel not used by user group_tool Used to get a list of groups related to fencing DLM GFS and getting debug information includes what cman_tool services provided in RHEL 4 groupd Daemon started by cman init script ...

Page 69: ...for machines controlled by IPMI Intelligent Platform Management Interface over LAN fence_wti Fence agent for WTI power switch fence_brocade Fence agent for Brocade Fibre Channel switch fence_mcdata Fence agent for McData Fibre Channel switch fence_vixel Fence agent for Vixel Fibre Channel switch fence_sanbox2 Fence agent for SANBox2 Fibre Channel switch fence_ilo Fence agent for HP ILO interfaces ...

Page 70: ... that repairs an unmounted GFS file system gfs_grow Command that grows a mounted GFS file system gfs_jadd Command that adds journals to a mounted GFS file system gfs_mkfs Command that creates a GFS file system on a storage device gfs_quota Command that manages quotas on a mounted GFS file system gfs_tool Command that configures or tunes a GFS file system This command can also gather a variety of i...

Page 71: ...ilover pulse on the backup LVS router instructs the pulse daemon on the active LVS router to shut down all LVS services starts the send_arp program to reassign the floating IP addresses to the backup LVS router s MAC address and starts the lvs daemon lvsd The lvs daemon runs on the active LVS router once called by pulse It reads the configuration file etc sysconfig ha lvs cf calls the ipvsadm util...

Page 72: ...ult tool to maintain the etc sysconfig ha lvs cf LVS configuration file send_arp This program sends out ARP broadcasts when the floating IP address changes from one node to another during failover Quorum Disk qdisk A disk based quorum daemon for CMAN Linux Cluster mkqdisk Cluster Quorum Disk Utility qdiskd Cluster Quorum Disk Daemon Table 2 1 Red Hat Cluster Suite Software Subsystem Components 2 M...

Page 73: ...e_egenera 8 I O Fencing agent for the Egenera BladeFrame fence_gnbd 8 I O Fencing agent for GNBD based GFS clusters fence_ilo 8 I O Fencing agent for HP Integrated Lights Out card fence_ipmilan 8 I O Fencing agent for machines controlled by IPMI over LAN fence_manual 8 program run by fenced as a part of manual I O Fencing fence_mcdata 8 I O Fencing agent for McData FC switches fence_node 8 A progr...

Page 74: ...S filesystem gfs_jadd 8 Add journals to a GFS filesystem gfs_mount 8 GFS mount options gfs_quota 8 Manipulate GFS disk quotas gfs_tool 8 interface to gfs ioctl calls Cluster Logical Volume Manager clvmd 8 cluster LVM daemon lvm 8 LVM2 tools lvm conf lvm 5 Configuration file for LVM2 lvmchange 8 change attributes of the logical volume manager pvcreate 8 initialize a disk or partition for use by LVM...

Page 75: ...table from stdin ipvsadm save 8 save the IPVS table to stdout nanny 8 tool to monitor status of services in a cluster send_arp 8 tool to notify network of a new IP address MAC address mapping 3 Compatible Hardware For information about hardware that is compatible with Red Hat Cluster Suite components for example supported fence devices storage devices and Fibre Channel switches refer to the hardwa...

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Page 77: ... requirements hardware 33 requirements network 33 requirements software 33 routing methods NAT 32 three tiered high availability cluster 30 M man pages cluster components 62 N NAT routing methods LVS 32 network address translation see NAT O overview economy 17 performance 17 scalability 17 P Piranha Configuration Tool CONTROL MONITORING 44 EDIT MONITORING SCRIPTS Subsection 54 GLOBAL SETTINGS 46 l...

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