The deployment of a cluster with byte-level file replication as implemented by SafeKit is much more simple than a cluster with block-level disk replication. The following table explains why.
Simplicity of byte-level file replication vs block-level disk replication | ||
Architecture | Cluster with byte-level file replication | Cluster with block-level disk replication |
Product | SafeKit on Windows and Linux | Disks replication products |
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 replicated disk. Data in the system disk cannot be replicated. |
Data replication | Synchronous byte-level file replication. Replicate file modification operations generated by application activity. No meta data are replicated. Only data modified in files are replicated, not entire files (byte-level file replication). Synchronous replication to avoid data loss on failure. | Block level disk replication. Replicate all data modified inside a replicated disk. Application data plus meta data are replicated. For instance, last access time on a file is replicated (last access time is modified each time the file is read). |
Complexity of deployment | No - install a software on 2 servers | Yes - require specific IT skills to configure OS and replicated disk |
Failover | Just restart the application on the secondary server | Remount the file system on the replicated disk. Pass the recovery procedure on the file system. And then restart the application |
Failback | Automatic failback. Resynchronization of data on the secondary server without stopping the application on the primary server. No application failover while data are not resynchronized. Automatic failover and automatic failback video | All products are not at the same level of features |
Split brain and quorum | 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 | All products are not at the same level of features |
Suited for | Software editors which want to add a simple high availability option to their application | Enterprise with IT skills in clustering |
More information on a byte-level file replication cluster on Windows and Linux here.
High availability architectures comparison | ||
Feature | SafeKit cluster | Other clusters |
Software clustering vs hardware clustering | | |
Shared nothing vs a shared disk cluster | | |
Application High Availability vs Full Virtual Machine High Availability | Smooth upgrade of application and OS possible server by server (version N and N+1 can coexist) | Smooth upgrade not possible |
High availability vs fault tolerance | 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) | Software exception on both servers at the same time. Smooth upgrade not possible |
Synchronous replication vs asynchronous replication | | |
Byte-level file replication vs block-level disk replication | | |
Heartbeat, failover and quorum to avoid 2 master nodes | | |
Virtual IP address primary/secondary, network load balancing, failover | | |
Evidian SafeKit mirror cluster with real-time file replication and failover | ||
All clustering features | |
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Synchronous replication | |
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Fully automated failback procedure | |
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Replication of any type of data | |
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File replication vs disk replication | |
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File replication vs shared disk | |
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Remote sites and virtual IP address | |
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Quorum | |
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Active/active cluster | |
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Uniform high availability solution | |
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Evidian SafeKit farm cluster with load balancing and failover | ||
No load balancer or dedicated proxy servers or special multicast Ethernet address | |
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All clustering features | |
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Remote sites and virtual IP address | |
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Uniform high availability solution | |
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