What does High Availability mean?

In terms of computers HA means a system design protocol which ensures the availability of a resource in a given amount of time or any terms of measurement.

HA-Clustering and Failover

This is a computer cluster implemented for making a resource available all the time or reducing the downtime of the resource. For example, an application server serving the user requests continuously and in come point of time it stopped responding. In that time the users waiting for a response from the server should not get disappointed.

Here comes the clustering technology, the cluster configuration in the network transfers or redirects the user requests to the backup server. This process is called Failover.

High-availability-clustering

The Clustering Software

The clustering software plays main role in the successful functioning of the HA-Clusters. Everyone have a question of who maintains the information and transactions processed by the First Machine.

Yes, the clustering software does that for us. It will copy the last good known configuration from the machine which failed to complete its duty to the machine which is ready to serve for us.

Heart Beat of Clustering

HA clusters use a private Heart-Beat network. This network is responsible for monitoring the health status of all the nodes in the cluster.

HA-Clustering-Heart Beat

Split-Brain in Cluster network

The term “Split-Brain” technically explains the following scenario. When all the private network link goes down but the individual cluster nodes are still running, there is a possibility of confusion. Each node in the cluster may think that other node is down and will supply duplicate data. So this is a tedious configure the network to avoid split-brains.

Cluster Node Configurations

 These are the available clustering node configurations

 1. Active/Active – Traffic is directed to another existing node or balanced across all other nodes

2. Active/Passive – A complete new node is served when primary node fails

3.  N+1 – Serving a complete new node in the place of primary node and the new node    in the cluster must be capable of handling any services which the primary node handled with/without any special additional software.

4. N+M – Here more than one dedicated nodes are served for handling failovers.
This   may require high cost and maintenance.

5. N-to-1 – Here the backup node is serving temporarily until the primary node is brought back online. Then the running services are transferred to primary node.

6. N-to-N — A combination of Active/Active and N+M clusters, N to N clusters.

Requirements for a High Availability Clustering Environment

The HA-Clustering is widely used technology in Data centers and Industries where adaptive infrastructure is required. This requires high investment hence this is called as costly technology.

Below given are the minimum requirements for setting up a HA Clustered Environment.

1. You must be having suitable advanced application which is capable to support HA-C. Not all the applications can run in High Availability Environment.
2. The application should be capable of running its own multiple instances.
3. The application you are using in HA-C must have command line utility. i.e ability to control the app through command line interface by executing some commands.
4. The application should have the capability of using Storage Area Network (SAN).

The application must be capable of storing the data in a SAN, so that even a crash occurs the other back-up node can use the saved-state of information.

Applications of HA Clustering Technology

So, where is this clustering more useful and applied ? HA Clustering is used for

1. Critical databases

2. File sharing networks

3. Business Applications

4. E-Commerce Websites

Some famous HA-Clustering products

My next update in HA-Clustering would be about configuring the HA clusters in live environment.

Wait for a couple days….

Regards,
R.Gopinath

What is  Logical Volume Manager ?

HP-UX LVM is used to manage disk space with special features like mirroring, high availability, stripping, etc. Physical volumes can be organized into a logical volume groups with equal size extent.

Each volume group can have one or more physical volumes. A system can have more than single volume groups. A volume group can be moved from a system to another instead of physical disk.

A volume group can be divided into virtual disks, called logical volumes. A logical volume can span a number of physical volumes or represent only a portion of one physical volume. Disks can be added into logical volumes with different sizes.

The following commands are used to create, display and manipulate the LVM:

1. pvcreate

Creates physical volume to use in logical volume group.

Syntax:  pvcreate -f /dev/rdsk/c2tod1

2. pvdisplay

Displays information about physical volumes in LVM volume group.

Syntax:  pvdisplay /dev/dsk/c2tod1

3. pvmove

Move allocated physical extents frm one LVM physcal volume to another.

Syntax:  pvmove /dev/dsk/c1t0d0 PVG0

4. vgcreate

Creates LVM volume group.

Syntax:  Create a directory for volume group. 

mkdir /dev/vg00 

vgcreate -s 2 /dev/vg00 /dev/dsk/c1t0d0

5. vgdisplay

Display information about LVM volume groups.

Syntax:  vgdisplay -v /dev/vg00

6. vgexport

Export an LVM volume group and its associated logical volumes.

Syntax:  vgexport -v -f vg00.outfile /dev/vg00

7. vgimport

Import an LVM volume group onto the system.

Syntax: vgimport -v /dev/vg00 /dev/dsk/c0t1d0

8. vgextend

Extend an LVM volume group by adding physical volumes.

Syntax:  vgextend /dev/vg00 /dev/dsk/c0t1d0

9. vgreduce

Remove physical volumes from an LVM volume group.

Syntax:  vgreduce /dev/vg00 /dev/dsk/c0t1d0

10. vgremove

Remove LVM logical volume group from system.

Syntax:  vgremove /dev/vg00 /dev/dsk/c0t1d0

11. vgscan

Scans physcal volumes for LVM volume group.

Syntax: vgscan

12. lvcreate

Creates logical volume in LVM volume group.

Syntax: 

lvcreate -L 100 /dev/vg03

13.  lvdisplay

Displays information about logical volumes .

lvdisplay /dev/vg00

14. lvextend

Increase space,mirrors for logical volumes.

lvextend -L 400 /dev/vg03

15.  lvreduce

Reduce number of physical extents, mirrors.

lvreduce -L 50 /dev/vg03

16. lvremove

Remove one or more logical volumes from system.

lvremove -f /dev/vg03

17. lvlnboot

Prepare LVM logical volume to be root, boot, primary swap, or dump volume.

lvlnboot -r /dev/vg00

18. lvrmboot

Remove logical volume link to root, primary swap, or dump volume.

lvrmboot -r /dev/vg00

Regards,
R.Gopinath

Introduction to vPartitions

vPars Is a Virtual Partitions product that enables you to run multiple instances of HP-UX simultaneously on one hard partition by dividing that hard partition further into virtual partitions.

Each virtual partition is assigned its own subset of hardware, runs a separate instance of HP-UX, and hosts its own set of applications. Because each instance of HP-UX is isolated from all other instances, vPars provides applicationand Operating System (OS) fault isolation.

Each instance of HP-UX can have different patches and a different kernel .

vPar-Representation

Key Terms of vPar

 

Complex:

A complex is the entire partitionable server, including both cabinets, all cells, I/O chassis, cables, and power and utility components.

Cabinet

A cabinet is the Superdome hardware “box”, which contains the cells, Guardian Service Processor (GSP), internal I/O chassis, I/O fans, cabinet fans, and power supplies. A complex has up to two cabinets.

Hard partition

A hard partition is any isolated hardware environment, such as an nPartition within a Superdome complex or an entire rp7400/N4000 server.

npartition

An nPartition is a subset of a complex that divides the complex into groups of cell boards where each group operates independently of other groups. An nPartition can run a single instance of HP-UX or be further divided into virtual partitions.

Virtual partition

A virtual partition is a software partition of a hard partition that contains an instance of

HP-UX. Though a hard partition can contain multiple virtual partitions, a virtual partition cannot span a hard partition boundary.

vPars Monitor and Database

vPars 

For each hard partition, the vPars Monitor manages the assignment of hardware resources to virtual partitions, boots virtual partitions and their kernels, and emulates certain firmware calls. By emulating these specific calls, vPars creates the illusion to each HP-UX instance that it is running on a standalone server, consisting of the hardware that has been assigned to it.

Once a virtual partition is launched, the Monitor transfers ownership of the hardware to the virtual partition. At that point the Monitor is not involved in accessing I/O hardware, physical memory, or process to processor cycles: the individual HP-UX instances have complete ownership of their respective hardware resources. This allows each partition to run at full speed.

vPars Partition Database

At the heart of the vPars Monitor is the partition database. The partition database contains partition configuration information. Using the partition database, the Monitor tracks which virtual partitions exist and what hardware resources and partition attributes are associated with each partition.

When the Monitor boots , it reads a copy of the partition database from a file on the same disk from which the Monitor /stand/vpmon is booted. The default file is /stand/vpdb. Then, the Monitor creates a master copy of the vPars partition database in the memory reserved by the Monitor.

The operating system of each virtual partition also keeps a local copy of the partition database in a file, by default /stand/vpdb, on its local boot disk

 Boot Sequence

This section describes the boot differences in a vPars system relative to a non-vPars system.

Boot Sequence: Quick Reference

On a server without vPars, a simplified boot sequence is:

 

 

 

vPar-boot-sequence

 

 

Adding vPars adds the Monitor layer, so now hpux (for Integrity, hpux.efi) loads the Monitor.

Then the Monitor boots the kernels of the virtual partitions. The boot sequence becomes

 

 

 

vPar-boot

 

 

Introduction to nPartitions

Cell-based HP servers enable you to configure a single server complex as one large system or as multiple smaller systems by configuring nPartition

• Each nPartition defines a subset of server hardware resources to be used as an independent system environment. An nPartition includes one or more cells assigned to it (with processors and memory) and all I/O chassis connected to those cells.

• All processors, memory, and I/O in an nPartition are used exclusively by software running in the nPartition.

• Each nPartition has its own system boot interface, and each nPartition boots and reboots independently.

• nPartitions can be reconfigured for a server without physically modifying the serverhardware configuration by using the HP software-based nPartition management tools.

Operating Systems Supported on nPartitions

Here is the list of operating systems that can run on nPartitions.

HP-UX 11i v1 (B.11.11)

HP-UX 11i v2 (B.11.23)

HP-UX 11i v3 (B.11.31)

HP OpenVMS I64 8.2-1 and 8.3

Microsoft® Windows® Server 2003

Red Hat Enterprise Linux

SuSE Linux Enterprise Server 9

SuSE Linux Enterprise Server 10

Administration Tools for nPartitions

The main administration tools for nPartitions are

1. Partition Manager – which provides a graphical interface.

2. The nPartition Commands – which provide a command-line interface.

Partition Manager

Tool location of Partition Manager (/opt/parmgr/bin/parmgr)

Partition Manager provides a graphical interface for configuring, modifying, and managing nPartitions and hardware within a server complex.

The following tools can perform nPartition administration tasks:

Service Processor (MP or GSP) Menus

Service processor menus provide a service interface for the entire complex. It allows access to all hardware and nPartitions defined within the complex.

EFI Boot Manager and EFI Shell Commands

On cell-based HP Integrity servers, the Extensible Firmware Interface (EFI) supports nPartition management. The EFI is accessible from an nPartition console when the nPartition is in an active state but has not booted an operating system.

BCH Menu Commands

On cell-based PA-RISC servers, the Boot Console Handler (BCH) interface supports management from an nPartition console when the nPartition is in an active state but has not booted an operating system.

nPartition Commands

Table:  nPartion Commands Description

nPartition Properties

This section describes the nPartition properties when work with performing nPartition administration tasks.

The following nPartitions details are covered here:

Partition Numbers

Each nPartition has its own unique partition number that the nPartition administration tools use for identifying the nPartition.

Assigned and Unassigned Cells

Each cell in a server complex either is assigned to one of the nPartitions in the complex, or it is unassigned and thus is not used by any of the nPartitions. If an I/O chassis is attached to an unassigned cell, then the chassis likewise is not assigned to an nPartition.

Base Cells

On both HP 9000 servers and HP Integrity servers, all cells within an nPartition are base cells. The nPartitions administration tools automatically set the cell type to base cell, if you do not specify the cell type

Core Cells

 One cell in each nPartition must serve as the active core cell. The core cell controls the nPartition until an operating system has booted, and it provides console services and other boot and management abilities for the nPartition.

The monarch processor on the core cell runs the Boot Console Handler (BCH) or Extensible Firmware Interface (EFI) code while all other processors are idle until an operating system is booted.

Active and Inactive Cells

Cells that are assigned to an nPartition and have booted to form an nPartition are active cells whose resources (processors, memory, and any attached I/O) can be actively used by software running in the nPartition.

Cells that are inactive either are not assigned to an nPartition, or they have not participated in partition rendezvous to form an nPartition with any other cells assigned to the nPartition.

Creating and Configuring nPartitions

Creating a New Partition

parcreate -c — command to create a new nPartition with the cells.

For example, with the Original nPartition Commands, the following command creates a

one-cell nPartition:

# parcreate -c4:base:y:ri -c6:base:y:ri

Partition Created. The partition number is : 1

#

When parcreate successfully creates a new nPartition, it reports “Partition Created” and reports the nPartition number (“partition number is…”).

If parcreate detects any problems or issues when creating an nPartition, it lists them in its output. If it cannot create the nPartition, parcreate reports “Command failed” along with more details.

Removing (Deleting) an nPartition

Deleting an nPartition causes all cells (and any I/O resources connected to the cells) that were assigned to the nPartition to be unassigned. As a result, all of these cells become available resources which can be assigned to any nPartition in the server complex.

When removing an active nPartition, you must complete the procedure by performing a shutdown for reconfig (the HP-UX shutdown -R -H command or Windows shutdown /s command) as soon as possible after initiating the nPartition removal.

1. Issue the parremove -p# command to remove the inactive remote nPartition

(-p# where # is the nPartition number).

For example:

#parremove -p1

2. Issue the parstatus -P command to confirm that the nPartition was removed.

If the nPartition was removed, it no longer is listed in the parstatus command output.

Renaming an nPartition

Use the parmodify -p# -P name command to set the nPartition name for any of the nPartitions in the server complex.

Specify both the nPartition number (-p#, where # is the nPartition number) and the new

name for the nPartition (-P name).

If the nPartition name contains spaces then quotation marks must surround the name.

# parmodify -p1 -P “New Name”

Command succeeded.

#

Booting and Resetting nPartitions

Types of Booting and Resetting for nPartitions

 HP cell-based servers provide two special types of reboot and reset for managing nPartitions: performing a reboot for reconfig, and performing a shutdown for reconfig.

Regards,
R.Gopinath