Evidian SafeKit brings high availability to Microsoft SQL Server. This article explains how to implement quickly a Microsoft SQL Server cluster without shared disk and without specific skills. The high availabity module sqlserver.safe and a free trial are offered in the installation instructions section.
Note that you can implement with the same product real-time replication and failover of other applications (database or other): see examples of mirror modules here.
This clustering solution is recognized as the simplest to implement by our customers and partners. It is also a complete solution that solves hardware failures (20% of problems) including the complete failure of a computer room, software failures (40% of problems) including smooth upgrade server by server and human errors (40% of problems) thanks to its simplicity of administration.
On the previous figure, the server 1/PRIM runs Microsoft SQL Server services (any edition). Users are connected to the virtual IP address of the mirror cluster. SafeKit replicates files opened by Microsoft SQL Server services in real time. Only changes in the files are replicated across the network, thus limiting traffic (byte-level file replication). Names of file directories containing Microsoft SQL Server services data are simply configured in SafeKit. There are no pre-requisites on disk organization for the two servers. Directories to replicate may be located in the system disk. SafeKit implements synchronous replication with no data loss on failure contrary to asynchronous replication.
In case of server 1 failure, there is an automatic failover on server 2 with restart of Microsoft SQL Server services. Then, when server 1 is restarted, SafeKit implements automatic failback with reintegration of data without stopping Microsoft SQL Server services on server 2. Finally, the system returns to synchronous replication between server 2 and server 1. The administrator can decide to swap the role of primary and secondary and return to a server 1 running Microsoft SQL Server services. The swap can also be done automatically by configuration.
Note that SafeKit is able to automatically re-synchronize a failed server without any manual operation and without stopping the critical application. It is an important differentiator when comparing SafeKit to replication solutions whose failover only works once: reintegrating the failed server in the cluster requires complex and non-automated manual operations.
Click on the Windows or Linux module to understand and try the solution
Mirror modules (replication and failover)
|Microsoft SQL Server||-|
|Milestone XProtect (based on Microsoft SQL Server)||-|
|Hanwha SSM (based on PostgreSQL)||-|
|Generic mirror module|
Farm modules (load balancing and failover)
|Generic farm module|
Click on the mirror/farm architecture to understand and try the solution
Real-time replication and failover cluster
Load balancing and failover cluster
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.
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.
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.
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.
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.
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 Microsoft SQL Server services.
For a software failure or an administrator restart, RTO = time to (cleanly) stop Microsoft SQL Server 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.
On both Windows servers
The configuration is presented with the web console connected to 2 Windows servers.
Important: all the configuration is made from a single browser.
Launch the web console in a browser by connecting to http://localhost:9010 (next image)
Enter IP address of the first node and click on Confirm (next image)
Click on New node and enter IP address of the second node (next image)
Click on the red floppy disk to save the configuration (previous image)
In the Configuration tab, click on sqlserver.safe (xxx.safe in the next image) then enter sqlserver as the module name and Confirm
Click on Validate (next image)
Change the path of replicated directories only if necessary (next image) and enter a virtual IP address. A virtual IP address is a new unused IP address in the same IP network as the IP addresses of the two nodes. The virtual IP address automatically switches in case of failover.
Click on Validate (previous image)
Click on Configure (previous image)
Check the success green message on both servers and click on Next (previous image).
Select the node with the most up-to-date replicated directories and click on start it to make the first resynchronization in the right direction (previous image). Before this operation, we suggest you to make a copy of replicated directories before starting the cluster to avoid any errors.
Start the second node (previous image) which becomes SECOND green (next image) after resynchronisation of all replicated directories (binary copy from node 1 to node 2).
The cluster is operational with Microsoft SQL Server services running on the PRIM node and nothing running on the SECOND node (previous image). Only modifications inside files are replicated in real-time in this state.
Be careful, components which are clients of the Microsoft SQL Server services must be configured with the virtual IP address. The configuration can be made with a DNS name (if a DNS name has been created and associated with the virtual IP address).
Check with Windows Microsoft Management Console (MMC) that the Microsoft SQL Server services are started on the primary server and stopped on the secondary server.
Stop the PRIM node by scrolling down the menu of the primary node and by clicking on Stop. Check that there is a failover on the SECOND node. And check the failover of Microsoft SQL Server services with Windows Microsoft Management Console (MMC).
To understand what happens in the cluster, check the SafeKit logs of the primary server and the secondary server.
To see the module log of the primary server (next image):
To see the application log of the primary server (next image):
To see the logs of the secondary server (previous image), click on W12R2server75/SECOND (it will become blue) on the left side and repeat the same operations. In the secondary module log, you will find the volume and the reintegration time of replicated data.
In Advanced Configuration tab (next image), you can edit internal files of the module: bin/start_prim and bin/stop_prim and conf/userconfig.xml (next image on the left side). If you make change in the internal files here, you must apply the new configuration by a right click on the blue icon/xxx on the left side (next image): the interface will allow you to redeploy the modified files on both servers.
Configure boot start (next image on the right side) configures the automatic boot of the module when the server boots. Do this configuration on both servers once the high availability solution is correctly running.
For getting support on the call desk of https://support.evidian.com, get 2 Snaphots (2 .zip files), one for each server and upload them in the call desk tool (next image).
<!DOCTYPE safe> <safe> <service mode="mirror" defaultprim="alone" maxloop="3" loop_interval="24" failover="on"> <!-- Heartbeat Configuration --> <!-- Names or IP addresses on the default network are set during initialization in the console --> <heart pulse="700" timeout="30000"> <heartbeat name="default" ident="flow"> </heartbeat> </heart> <!-- Virtual IP Configuration --> <!-- Replace * VIRTUAL_TO_BE_DEFINED by the name of your virtual server --> <vip> <interface_list> <interface check="on" arpreroute="on"> <real_interface> <virtual_addr addr="VIRTUAL_TO_BE_DEFINED" where="one_side_alias" /> </real_interface> </interface> </interface_list> </vip> <!-- Software Error Detection Configuration --> <errd polltimer="10"> <!-- Microsoft SQL Server process --> <proc name="sqlservr.exe" atleast="1" action="restart" class="prim" /> <proc name="sqlagent.exe" atleast="1" action="restart" class="prim" /> <proc name="sqlwriter.exe" atleast="1" action="restart" class="prim" /> </errd> <!-- File Replication Configuration --> <!-- Replace * YOUR_INSTANCE to set the directory of your Microsoft SQL Server database and logs --> <rfs async="second" acl="off" nbrei="3"> <replicated dir="C:\Program Files\Microsoft SQL Server\YOUR_INSTANCE\MSSQL\DATA" mode="read_only" /> <replicated dir="C:\Program Files\Microsoft SQL Server\YOUR_INSTANCE\MSSQL\Log" mode="read_only" /> </rfs> <!-- User scripts activation --> <user nicestoptimeout="300" forcestoptimeout="300" logging="userlog" /> </service> </safe>
@echo off rem Script called on the primary server for starting application services rem For logging into SafeKit log use: rem "%SAFE%\safekit" printi | printe "message" rem stdout goes into Application log echo "Running start_prim %*" set res=0 net start "MSSQLServer" > nul if not %errorlevel% == 0 ( %SAFE%\safekit printi "MSSQLServer start failed" ) else ( %SAFE%\safekit printi "MSSQLServer started" ) net start "SQLServerAgent" > nul if not %errorlevel% == 0 ( %SAFE%\safekit printi "SQLServerAgent start failed" ) else ( %SAFE%\safekit printi "SQLServerAgent started" ) net start "SQLWriter" > nul if not %errorlevel% == 0 ( %SAFE%\safekit printi "SQLWriter start failed" ) else ( %SAFE%\safekit printi "SQLWriter started" ) if %res% == 0 goto end :stop set res=%errorlevel% "%SAFE%\safekit" printe "start_prim failed" rem uncomment to stop SafeKit when critical rem "%SAFE%\safekit" stop -i "start_prim" :end
@echo off rem Script called on the primary server for stopping application services rem ---------------------------------------------------------- rem rem 2 stop modes: rem rem - graceful stop rem call standard application stop with net stop rem rem - force stop (%1=force) rem kill application's processes rem rem ---------------------------------------------------------- rem For logging into SafeKit log use: rem "%SAFE%\safekit" printi | printe "message" rem stdout goes into Application log echo "Running stop_prim %*" set res=0 rem default: no action on forcestop if "%1" == "force" goto end %SAFE%\safekit printi "Stopping SQLServerAgent..." net stop "SQLServerAgent" > nul %SAFE%\safekit printi "Stopping MSSQLServer..." net stop "MSSQLServer" > nul %SAFE%\safekit printi "Stopping SQLWriter..." net stop "SQLWriter" > nul rem wait a little for a real stop of services %SAFEBIN%\sleep 10 :end