Shared nothing cluster vs shared disk cluster is an important point to consider when choosing a cluster solution. The deployment of a shared nothing cluster as implemented by SafeKit is much more simple than a shared disk cluster.
Simplicity of a shared nothing vs a shared disk cluster | ||
| Architecture | Shared nothing cluster
| Shared disk cluster
|
| Product | SafeKit on Windows 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. All data to recover must be localized in a special shared disk. Data in the system disk cannot be replicated. |
| 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. Video of disaster recovery with a software SAN | Extra cost with a second bay of disks.New specific IT skills to configure mirroring of bays across a SAN. |
| Quorum and split brain | No data corruption in case of network isolation between the two servers (split brain). Cluster quorum video : no quorum server and no quorum disk | 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 availabity to their application | Enterprise with IT skills and large database applications |
More information on shared nothing clusters implemented by the SafeKit software on Windows and Linux here.
In video surveillance systems, Evidian SafeKit implements high availability with synchronous replication and failover of
Harmonic is using SafeKit as a software OEM high availability solution and deploys it with its TV broadcasting solutions over satellites, terrestrials, cable, IPTV. Over 80 SafeKit clusters are deployed on Windows for replication of Harmonic database and automatic failover of the critical application. Philippe Vidal, Product Manager, Harmonic says: “SafeKit is the ideal application clustering solution for a software publisher looking for a simple and economical high availability software. We are deploying SafeKit worldwide and we currently have more than 80 SafeKit clusters on Windows with our critical TV broadcasting application through terrestrial, satellite, cable and IP-TV. SafeKit implements the continuous and real-time replication of our database as well as the automatic failover of our application for software and hardware failures. Without modifying our application, it was possible for us to customize the installation of SafeKit. Since then, the time of preparation and implementation has been significantly reduced.”
The European Society of Warranties and Guarantees in Natixis uses SafeKit as a high availability solution for its applications.
Over 30 SafeKit clusters are deployed on Unix and Windows in Natixis.
Fives Syleps, the Sydel software editor implements high availability of its ERP with SafeKit and deploys the solution in the food industry.
Over 20 SafeKit clusters are deployed on Unix with Oracle.
Air traffic control systems supplier, Copperchase, deploys SafeKit high availability in airports.
Over 20 SafeKit clusters are deployed on Windows.
Tony Myers, Director of Business Development says:
“By developing applications for air traffic control, Copperchase is in one of the most critical business activities. We absolutely need our applications to be available all the time. We have found with SafeKit a simple and complete clustering solution for our needs. This software combines in a single product load balancing, real time data replication with no data loss and automatic failover. This is why, Copperchase deploys SafeKit for air traffic control in airports in the UK and the 30 countries where we are present.”
Software vendor Wellington IT deploys SafeKit high availability with its banking application for Credit Unions in Ireland and UK.
Over 25 SafeKit clusters are deployed on Linux with Oracle.
Peter Knight, Sales Manager says:
“Business continuity and disaster recovery are a major concern for our Locus banking application deployed in numerous Credit Unions around Ireland and the UK. We have found with SafeKit a simple and robust solution for high availability and synchronous replication between two servers with no data loss. With this software solution, we are not dependent on a specific and costly hardware clustering solution. It is a perfect tool to provide a software high availability option to an application of a software vendor.”
Paris transport company (RATP) chose the SafeKit high availability and load balancing solution for the centralized control room of line 1 of the Paris subway.
20 SafeKit clusters are deployed on Windows and Linux.
Stéphane Guilmin, RATP, Project manager says:
“Automation of line 1 of the Paris subway is a major project for RATP, requiring a centralized command room (CCR) designed to resist IT failures. With SafeKit, we have three distinct advantages to meet this need. Firstly, SafeKit is a purely software solution that does not demand the use of shared disks on a SAN and network boxes for load balancing. It is very simple to separate our servers into separate machine rooms. Moreover, this clustering solution is homogeneous for our Windows and Unix platforms. SafeKit provides the three functions that we needed: load balancing between servers, automatic failover after an incident and real time data replication.”
And also, Philippe Marsol, Atos BU Transport, Integration Manager says:
“SafeKit is a simple and powerful product for application high availability. We have integrated SafeKit in our critical projects like the supervision of Paris metro Line 4 (the control room) or Marseille Line 1 and Line 2 (the operations center). Thanks to the simplicity of the product, we gained time for the integration and validation of the solution and we had also quick answers to our questions with a responsive Evidian team.”
The software integrator Systel deploys SafeKit high-availability solution in firefighter and emergency medical call centers.
Over 30 SafeKit clusters are deployed on Windows with SQL Server.
Marc Pellas, CEO says:
“SafeKit perfectly meets the needs of a software vendor. Its main advantage is that it brings in high availability through a software option that is added to our own multi-platform software suite. This way, we are not dependent on a specific and costly hardware clustering solution that is not only difficult to install and maintain, but also differs according to client environments. With SafeKit, our firefighter call centers are run with an integrated software clustering solution, which is the same for all our customers, is user friendly and for which we master the installation up to after-sales support.”
ERP high availability and load balancing of the French army (DGA) are made with SafeKit.
14 SafeKit clusters are deployed on Windows and Linux.
Alexandre Barth, Systems administrator says:
“Our production team implemented the SafeKit solution without any difficulty on 14 Windows and Linux clusters. Our critical activity is thus secure, with high-availability and load balancing functions. The advantages of this product are easy deployment and administration of clusters, on the one hand, and uniformity of the solution in the face of heterogeneous operating systems, on the other hand.”
| OEM Software | Distributed Enterprise | Remote Sites |
 |  |  |
| A software publisher uses SafeKit as an OEM software for high availability of its application | A distributed enterprise deploys SafeKit in many branches without specific IT skills | SafeKit is deployed in two remote sites without the need for replicated bays of disks through a SAN |
1 - The ideal product for a software publisher | ||
“SafeKit is the ideal application clustering solution for a software publisher. We currently have deployed more than 80 SafeKit clusters worldwide with our critical TV broadcasting application.” | ||
2 - The product very easy to deploy for a reseller | ||
“WithNCompany has deployed in South Korea many SafeKit high availability solutions with the Samsung Video Surveillance Platform. SafeKit is appreciated because the product is easy to install and very quickly deployed.” | ||
3 - The product to gain time for a system integrator | ||
“Thanks to a simple and powerful product, we gained time in the integration and validation of our critical projects like the supervision of Paris and Marseille metro lines (the control rooms).” | ||
High availability architectures comparison(click on the feature for more information) | ||
| Feature | SafeKit cluster | Other clusters |
| Software clustering vs hardware clustering |  A simple software cluster with the SafeKit package installed on two servers |   Complex hardware clustering with external storage or network load balancers |
| Shared nothing vs a shared disk cluster |  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 |  SafeKit application HA supports hardware failure, software failure, human errors with quick recovery time |  Full virtual machines HA supports only hardware failure with a VM reboot and an unknown recovery time if the OS reboot does not work |
| Synchronous replication vs asynchronous replication | 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 | SafeKit implements byte-level file replication and is simply configured with 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 |  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 |
| Network load balancing |  No special network configuration is required in a SafeKit cluster for network load balancing |  Special network configuration is required in other clusters for network load balancing |
RTO is the time during which the application is unavailable in case of failure. RTO of the SafeKit mirror solution is in the order of 1 mn.
For a hardware failure, RTO = heartbeat timeout (default 30 s, can be changed in userconfig.xml) + time to restart services.
For a software failure or an administrator restart, RTO = time to (cleanly) stop services + time to restart them.
Be careful, with solutions that reboot a full virtual machine in case of failure, the RTO is unpredictable as manual operations may be required after a hardware crash to reboot the virtual machine.
RPO reflects the data loss in case of failure. RPO of the SafeKit mirror solution is 0 as the replication is synchronous and real-time.
Be careful, with asynchronous replication, RPO is not 0 and there is data loss in case of failure when the application restarts on the secondary server.
RTO is the time during which the application is unavailable in case of failure. RTO of the SafeKit farm solution is in the order of a few seconds on hardware failure.
For a hardware failure, RTO = failure detection timeout through monitoring channels (default a few seconds): after the timeout the load balancing filters are reconfigured.
For a software failure or an administrator restart, RTO = time to (cleanly) stop services + time to restart them.
