Data replication techniques

What is the data replication technique at database level?

It is the replication of log files between two servers made by the database management system (like the SQL Server log).

For an automatic failover, it is mandatory to have synchronous replication otherwise the data of the last validated transactions will not be recovered on the secondary server after a failover.

This data replication technique replicates a database but not the other data of an application. Failover of many applications also requires the replication of other data such as configuration files.

When a server crashes and loses some database files, failback is not automatic. A skilled DBA must restore the database on the failed server.

What is the data replication technique at disk level?

It is the replication of modifications inside disks between two servers (like DRBD).

For an automatic failover, synchronous replication between the disks is mandatory for having 0 data loss.

This data replication technique can replicate databases as well as other files. But, there is a strong impact on the organization of application data. All data must be localized in the relicated disk. This may be impossible if some data to replicate are in the system disk, because this disk must remain specific to each server.

Skills are required to configure a replicated disk with a file system and to configure application data in the replicated disk.

What is the data replication technique at file level?

It is the replication of modifications inside files between two servers (like SafeKit).

For an automatic failover, real-time synchronous replication is required for having 0 data loss.

This data replication technique can replicate databases as well as other files. There is no impact on data organization for an application. For instance, if an application has its data in the system disk, real-time file replication is working.

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

Pros and cons of data replication techniques on the SafeKit example

Evidian SafeKit mirror cluster with real-time file replication and failover
3 products in 1 More info >	The SafeKit high availability software saves on Windows and Linux the cost of : external shared or replicated storage, load balancing boxes, enterprise editions of OS and databases SafeKit includes all clustering features: synchronous real-time file replication, monitoring of server / network / software failures, automatic application restart, virtual IP address switched in case of failure to reroute clients
Very simple configuration More info >	The cluster configuration is very simple and made by means of application modules. New services and new replicated directories can be added to an existing application module to complete a high availability solution All the configuration of clusters is made using a simple centralized web administration console There is no domain controller or active directory to configure as with Microsoft cluster
Synchronous replication More info >	The real-time replication is synchronous with no data loss on failure This is not the case with asynchronous replication
Fully automated failback More info >	After a failure when a server reboots, the replication failback procedure is fully automatic and the failed server reintegrates the cluster without stopping the application on the only remaining server This is not the case with most replication solutions particularly with replication at the database level. Manual operations are required for resynchronizing a failed server. The application may even be stopped on the only remaining server during the resynchonization of the failed server
Replication of any type of data More info >	The replication is working for databases but also for any files which shall be replicated This not the case for replication at the database level
File replication vs disk replication More info >	The replication is based on file directories that can be located anywhere (even in the system disk) This is not the case with disk replication where special application configuration must be made to put the application data in a special disk
File replication vs shared disk More info >	The servers can be put in two remote sites This is not the case with shared disk solutions
Remote sites and virtual IP address More info >	All SafeKit clustering features are working for 2 servers in remote sites. Replication requires an extended LAN type network (latency = performance of synchronous replication, bandwidth = performance of resynchronization after failure). If both servers are connected to the same IP network through an extended LAN between two remote sites, the virtual IP address of SafeKit is working with rerouting at level 2 If both servers are connected to two different IP networks between two remote sites, the virtual IP address can be configured at the level of a load balancer with the "healh check" of SafeKit.
Quorum and split brain More info >	The solution works with only 2 servers and for the quorum (network isolation between both sites), a simple split brain checker to a router is offered to support a single execution of the critical application This is not the case for most clustering solutions where a 3^rd server is required for the quorum
Active/active cluster More info >	The secondary server is not dedicated to the restart of the primary server. The cluster can be active-active by running 2 different mirror modules This is not the case with a fault-tolerant system where the secondary is dedicated to the execution of the same application synchronized at the instruction level
Uniform high availability solution More info >	SafeKit implements a mirror cluster with replication and failover. But it imlements also a farm cluster with load balancing and failover. Thus a N-tiers architecture can be made highly available and load balanced with the same solution on Windows and Linux (same installation, configuration, administration with the SafeKit console or with the command line interface). This is unique on the market This is not the case with an architecture mixing different technologies for load balancing, replication and failover
RTO / RPO More info >	SafeKit implements quick application restart in case of failure: around 1 mn or less Quick application restart is not ensured with full virtual machines replication. In case of hypervisor failure, a full VM must be rebooted on a new hypervisor with a recovery time depending on the OS reboot as with VMware HA or Hyper-V cluster

Key differentiators of the SafeKit high availability technology

Software clustering vs hardware clustering More info >
A simple software cluster with the SafeKit package just installed on two servers	Complex hardware clustering with external storage or network load balancers
Shared nothing vs a shared disk cluster More info >
SafeKit is a shared-nothing cluster: easy to deploy even in remote sites	A shared disk cluster is complex to deploy
Application High Availability vs Full Virtual Machine High Availability More info >
Application HA supports hardware failure and software failure with a quick recovery time (RTO around 1 mn or less). Application HA requires to define restart scripts per application and folders to replicate (SafeKit application modules).	Full virtual machines HA supports only hardware failure with a VM reboot and a recovery time depending on the OS reboot. No restart scripts to define with full virtual machines HA (SafeKit hyperv.safe or kvm.safe modules). Hypervisors are active/active with just multiple virtual machines.
High availability vs fault tolerance More info >
No dedicated server with SafeKit. Each server can be the failover server of the other one. Software failure with restart in another OS environment. Smooth upgrade of application and OS possible server by server (version N and N+1 can coexist)	Secondary server dedicated to the execution of the same application synchronized at the instruction level. Software exception on both servers at the same time. Smooth upgrade not possible
Synchronous replication vs asynchronous replication More info >
SafeKit implements real-time synchronous replication with no data loss in case of failure	With asynchronous replication, there is data loss on failure
Byte-level file replication vs block-level disk replication More info >
SafeKit implements real-time byte-level file replication and is simply configured with application directories to replicate even in the system disk	Block-level disk replication is complex to configure and requires to put application data in a special disk
Heartbeat, failover and quorum to avoid 2 master nodes More info >
To avoid 2 masters, SafeKit proposes a simple split brain checker configured on a router	To avoid 2 masters, other clusters require a complex configuration with a third machine, a special quorum disk, a special interconnect
Virtual IP address primary/secondary, network load balancing, failover More info >
No dedicated proxy servers and no special network configuration are required in a SafeKit cluster for virtual IP addresses	Special network configuration is required in other clusters for virtual IP addresses. Note that SafeKit offers a health check adapted to load balancers

Key differentiators of a farm cluster with load balancing and failover

Evidian SafeKit farm cluster with load balancing and failover
No load balancer or dedicated proxy servers or special multicast Ethernet address More info >	The solution does not require load balancers or dedicated proxy servers above the farm for imlementing load balancing. SafeKit is installed directly on the application servers in the farm. The load balancing is based on a standard virtual IP address/Ethernet MAC address and is working with physical servers or virtual machines on Windows and Linux without special network configuration This is not the case with network load balancers This is not the case with dedicated proxies on Linux This is not the case with a specific multicast Ethernet address on Windows
All clustering features More info >	The solution includes all clustering features: virtual IP address, load balancing on client IP address or on sessions, monitoring of server / network / software failures, automatic application restart with a quick revovery time and a replication option with a mirror module This is not the case with other load balancing solutions. They are able to make load balancing but they do not include a full clustering solution with restart scripts and automatic application restart in case of failure. They do not offer a replication option The cluster configuration is very simple and made by means of application modules. There is no domain controller or active directory to configure on Windows. The solution works on Windows and Linux
Remote sites and virtual IP address More info >	If servers are connected to the same IP network through an extended LAN between remote sites, the virtual IP address of SafeKit is working with load balancing at level 2 If servers are connected to different IP networks between remote sites, the virtual IP address can be configured at the level of a load balancer with the help of the SafeKit health check. Thus you can implement load balancing but also all the clustering features of SafeKit, in particular monitoring and automatic recovery of the critical application on application servers
Uniform high availability solution More info >	SafeKit imlements a farm cluster with load balancing and failover. But it implements also a mirror cluster with replication and failover. Thus a N-tiers architecture can be made highly available and load balanced with the same solution on Windows and Linux (same installation, configuration, administration with the SafeKit console or with the command line interface). This is unique on the market This is not the case with an architecture mixing different technologies for load balancing, replication and failover

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

Data replication techniques

Evidian SafeKit