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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

Comparison of SafeKit with Traditional High Availability (HA) Clusters

How does SafeKit compare to traditional High Availability (HA) cluster solutions?

This comparison highlights the fundamental differences between SafeKit and traditional High Availability (HA) cluster solutions like Failover Clusters, Virtualization HA, and SQL Always-On. SafeKit is designed as a low-complexity, software-only solution for generic application redundancy, contrasting with the high complexity and specific storage requirements (shared storage, SAN) typical of traditional HA mechanisms.
Comparison of SafeKit with traditional High Availability (HA) clusters
Solutions Complexity Comments
Failover Cluster (Microsoft) High Specific Storage (shared storage, SAN)
Virtualization (VMware HA) High Specific Storage (shared storage, SAN, vSAN)
SQL Always-On (Microsoft) High Only SQL is redundant, requires SQL Enterprise Edition
Evidian SafeKit Low Simplest, generic and software-only. Unsuitable for large data replication.

SafeKit's Advantage in Application Redundancy

SafeKit achieves its low-complexity High Availability through a simple, software-based mirroring mechanism that eliminates the need for expensive, dedicated hardware like a SAN (Storage Area Network). This makes it a highly accessible solution for quickly implementing application redundancy without complex infrastructure changes.

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 High Availability (HA) Solutions: Quick Installation Guides for Windows and Linux Clusters

This table presents the SafeKit High Availability (HA) solutions, categorized by application and operating environment (Databases, Web Servers, VMs, Cloud). Identify the specific pre‑configured .safe module (e.g., mirror.safe, farm.safe, and others) required for real‑time replication, load balancing, and automatic failover of critical business applications on Windows or Linux. Simplify your HA cluster setup with direct links to quick installation guides, each including a download link for the corresponding .safe module.

A SafeKit .safe module is essentially a pre‑configured High Availability (HA) template that defines how a specific application will be clustered and protected by the SafeKit software. In practice, it contains a configuration file (userconfig.xml) and restart scripts.

SafeKit High Availability (HA) Solutions: Quick Installation Guides (with downloadable .safe modules)
Application Category HA Scenario (High Availability) Technology / Product .safe Module Installation Guide
New Applications Real-Time Replication and Failover Windows mirror.safe View Guide: Windows Replication
New Applications Real-Time Replication and Failover Linux mirror.safe View Guide: Linux Replication
New Applications Network Load Balancing and Failover Windows farm.safe View Guide: Windows Load Balancing
New Applications Network Load Balancing and Failover Linux farm.safe View Guide: Linux Load Balancing
Databases Replication and Failover Microsoft SQL Server sqlserver.safe View Guide: SQL Server Cluster
Databases Replication and Failover PostgreSQL postgresql.safe View Guide: PostgreSQL Replication
Databases Replication and Failover MySQL mysql.safe View Guide: MySQL Cluster
Databases Replication and Failover Oracle oracle.safe View Guide: Oracle Failover Cluster
Databases Replication and Failover Firebird firebird.safe View Guide: Firebird HA
Web Servers Load Balancing and Failover Apache apache_farm.safe View Guide: Apache Load Balancing
Web Servers Load Balancing and Failover IIS iis_farm.safe View Guide: IIS Load Balancing
Web Servers Load Balancing and Failover NGINX farm.safe View Guide: NGINX Load Balancing
VMs and Containers Replication and Failover Hyper-V hyperv.safe View Guide: Hyper-V VM Replication
VMs and Containers Replication and Failover KVM kvm.safe View Guide: KVM VM Replication
VMs and Containers Replication and Failover Docker mirror.safe View Guide: Docker Container Failover
VMs and Containers Replication and Failover Podman mirror.safe View Guide: Podman Container Failover
VMs and Containers Replication and Failover Kubernetes K3S k3s.safe View Guide: Kubernetes K3S Replication
AWS Cloud Real-Time Replication and Failover AWS mirror.safe View Guide: AWS Replication Cluster
AWS Cloud Network Load Balancing and Failover AWS farm.safe View Guide: AWS Load Balancing Cluster
GCP Cloud Real-Time Replication and Failover GCP mirror.safe View Guide: GCP Replication Cluster
GCP Cloud Network Load Balancing and Failover GCP farm.safe View Guide: GCP Load Balancing Cluster
Azure Cloud Real-Time Replication and Failover Azure mirror.safe View Guide: Azure Replication Cluster
Azure Cloud Network Load Balancing and Failover Azure farm.safe View Guide: Azure Load Balancing Cluster
Physical Security / VMS Real-Time Replication and Failover Milestone XProtect milestone.safe View Guide: Milestone XProtect Failover
Physical Security / VMS Real-Time Replication and Failover Nedap AEOS nedap.safe View Guide: Nedap AEOS Failover
Physical Security / VMS Real-Time Replication and Failover Genetec (SQL Server) sqlserver.safe View Guide: Genetec SQL Failover
Physical Security / VMS Real-Time Replication and Failover Bosch AMS (Hyper-V) hyperv.safe View Guide: Bosch AMS Hyper-V Failover
Physical Security / VMS Real-Time Replication and Failover Bosch BIS (Hyper-V) hyperv.safe View Guide: Bosch BIS Hyper-V Failover
Physical Security / VMS Real-Time Replication and Failover Bosch BVMS (Hyper-V) hyperv.safe View Guide: Bosch BVMS Hyper-V Failover
Physical Security / VMS Real-Time Replication and Failover Hanwha Vision (Hyper-V) hyperv.safe View Guide: Hanwha Vision Hyper-V Failover
Physical Security / VMS Real-Time Replication and Failover Hanwha Wisenet (Hyper-V) hyperv.safe View Guide: Hanwha Wisenet Hyper-V Failover
Siemens Products Real-Time Replication and Failover Siemens Siveillance suite (Hyper-V) hyperv.safe View Guide: Siemens Siveillance HA
Siemens Products Real-Time Replication and Failover Siemens Desigo CC (Hyper-V) hyperv.safe View Guide: Siemens Desigo CC HA
Siemens Products Real-Time Replication and Failover Siemens Siveillance VMS SiveillanceVMS.safe View Guide: Siemens Siveillance VMS HA
Siemens Products Real-Time Replication and Failover Siemens SiPass (Hyper-V) hyperv.safe View Guide: Siemens SiPass HA
Siemens Products Real-Time Replication and Failover Siemens SIPORT (Hyper-V) hyperv.safe View Guide: Siemens SIPORT HA
Siemens Products Real-Time Replication and Failover Siemens SIMATIC PCS 7 (Hyper-V) hyperv.safe View Guide: SIMATIC PCS 7 HA
Siemens Products Real-Time Replication and Failover Siemens SIMATIC WinCC (Hyper-V) hyperv.safe View Guide: SIMATIC WinCC HA