Shared nothing architecture vs shared disk architecture

Evidian SafeKit

Shared nothing architecture vs shared disk architecture for high availability clusters

Overview

This article explores the pros and cons of shared nothing architecture vs shared disk architecture for high availability clusters. We are looking at hardware constraints, impact on application data organization, recovery time, simplicity of implementation.

Shared nothing architecture vs shared disk architecture

The following comparative tables explain in detail the difference between shared disk architecture and SafeKit, a software clustering product implementing a shared nothing architecture.

What is a shared disk architecture?

A shared disk architecture (like with Microsoft failover cluster) is based on 2 servers sharing a disk with an automatic application failover in case of hardware of software failures.

This architecture has hardware constraints: the specific external shared storage, the specific cards to install inside the servers, and the specific switches between the servers and the shared storage.

A shared disk architecture has a strong impact on the organization of application data. All application data must be localized in the shared disk for a restart after a failover.

Moreover, on failover, the file system recovery procedure must be executed on the shared disk. This increases the recovery time (RTO).

Finally, the solution is not easy to configure because skills are required to configure the specific hardware. Additionally, application skills are required to configure application data in the shared disk.

What is a shared nothing architecture ?

A shared nothing architecture (like with SafeKit) is based on 2 servers replicating data in real-time with an automatic application failover in case of hardware of software failures.

There are two types of data replication: byte level file replication vs block level disk replication. We consider here byte level file replication because it has many advantages against block level disk replication.

The shared nothing architecture has no hardware constraints: the servers can be physical or virtual with any type of disk organization. Real-time file replication (synchronous for having 0 data loss) is made through the standard network between servers.

This architecture has no impact on application data organization. For instance, if an application has its data in the system disk, real-time file replication is working.

Recovery time (RTO) in the event of a failover is reduced to the application restart time on the secondary server's replicated files.

Finally, the solution is very simple to configure as only the paths of directories to replicate are configured.

Pros and cons of shared nothing architecture vs shared disk architecture

Shared nothing architecture

Shared nothing architecture

Shared disk architecture

Shared disk architecture

Product

SafeKit on Windows and Linux

Clustering toolkit for shared disk

Extra hardware

No - Use internal disks of servers

Yes - Extra cost with a shared bay of disks

Application data organization

0 impact on application data organization with SafeKit.

Just define directories to replicate in real-time.

Even directories inside the system disk can be replicated.

Impact on application data organization.

Special configuration of the application to put its data in a shared disk.

Data in the system disk cannot be recovered.

Complexity of deployment

No - install a software on 2 servers

Yes - require specific IT skills to configure OS and shared disk

Failover

Just restart the application on the second server.

Switch the shared disk.

Remount the file system.

Pass the recovery procedure on the file system.

And then restart the application.

Disaster revovery

Just put the 2 servers in 2 remotes sites connected by an extended LAN.

Extra cost with a second bay of disks.

Specific IT skills to configure mirroring of bays across a SAN.

Quorum and split brain

Application executed on a single server after a network isolation (split brain).

Coherency of data after a split brain.

No need for a third machine or a quorum disk or a special heartbeat line for split brain.

More information on heartbeat, failover and quorum

Require a special quorum disk or a third quorum server to avoid data corruption on split brain

Suited for

Software editors which want to add a simple high availability option to their application

Enterprise with IT skills in clustering and with large database applications

SafeKit High Availability Differentiators against Competition

Video comparing a shared disk architecture and a shared nothing architecture when considering disaster recovery

Video content

This video first illustrates the work to be done with a shared disk architecture when the two servers of a high availability cluster must be placed on two remote sites.

Next, the video demonstrates the same use case with the SafeKt shared nothing architecture.

SafeKit: an ideal solution for a partner application

This platform agnostic solution is ideal for a partner with a critical application and who wants to provide a redundancy and high availability option easy to deploy to many customers.

This clustering solution is also recognized as the simplest to implement by our partners.

SafeKit Modules for Plug&Play Redundancy and High Availability Solutions

SafeKit Modules for Plug&Play High Availability Solutions

Network load balancing and failover

Windows farm

Linux farm

Generic Windows farm   > Generic Linux farm   >
Microsoft IIS   > -
NGINX   >
Apache   >
Amazon AWS farm   >
Microsoft Azure farm   >
Google GCP farm   >
Other cloud   >

Advanced clustering architectures

Several modules can be deployed on the same cluster. Thus, advanced clustering architectures can be implemented:

Demonstrations of Redundancy and High Availability Solutions

SafeKit Webinar

This webinar presents in 2 minutes Evidian SafeKit.

In this webinar, you will understand SafeKit mirror and farm clusters.

Microsoft SQL Server Cluster

This video shows a mirror module configuration with synchronous real-time replication and failover.

The file replication and the failover are configured for Microsoft SQL Server but it works in the same manner for other databases.

Free trial here

Apache Cluster

This video shows a farm module configuration with load balancing and failover.

The load balancing and the failover are configured for Apache but it works in the same manner for other web services.

Free trial here

Hyper-V Cluster

This video shows a Hyper-V cluster with full replications of virtual machines.

Virtual machines can run on both Hyper-V servers and they are restarted in case of failure.

Free trial here

SafeKit Training

Introduction

  1. Overview / pptx

    • Features
    • Architectures
    • Distinctive advantages
  2. Competition / pptx

    • Hardware vs software cluster
    • Synchronous vs asynchronous replication
    • File vs disk replication
    • High availability vs fault tolerance
    • Hardware vs software load balancing
    • Virtual machine vs application HA

Installation, Console, CLI

  1. Install and setup / pptx

    • Package installation
    • Nodes setup
    • Cluster configuration
    • Upgrade
  2. Web console / pptx

    • Cluster configuration
    • Configuration tab
    • Control tab
    • Monitor tab
    • Advanced Configuration tab
  3. Command line / pptx

    • Silent installation
    • Cluster administration
    • Module administration
    • Command line interface

Advanced configuration

  1. Mirror module / pptx

    • userconfig.xml + restart scripts
    • Heartbeat (<hearbeat>)
    • Virtual IP address (<vip>)
    • Real-time file replication (<rfs>)
  2. Farm  module / pptx

    • userconfig.xml + restart scripts
    • Farm configuration (<farm>)
    • Virtual IP address (<vip>)
  3. Checkers / pptx

    • Failover machine (<failover>)
    • Process monitoring (<errd>)
    • Network and duplicate IP checkers
    • Custom checker (<custom>)
    • Split brain checker (<splitbrain>)
    • TCP, ping, module checkers

Support

  1. Support tools / pptx

    • Analyze snapshots
  2. Evidian support / pptx

    • Get permanent license key
    • Register on support.evidian.com
    • Call desk

Documentation

  1. Technical documentation

  2. Presales documentation