Evidian > Products > High Availability Software - Zero Extra Hardware > Byte-level file replication vs block-level disk replication
Cluster with byte-level file replication |
Cluster with block-level disk replication |
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Disks replication products |
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Application data organization |
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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 |
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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). |
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 |
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No - install a software on 2 servers |
Yes - require specific IT skills to configure OS and replicated disk |
Failover |
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Just restart the application on the second server. |
Remount the file system on the replicated disk. Pass the recovery procedure on the file system. And then restart the application. |
Failback |
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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. |
All products are not at the same level of features. |
Quorum and split brain |
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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. |
Require a special quorum disk or a third quorum server to manage split brain. |
Suited for |
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Software editors which want to add a simple high availability option to their application |
Enterprise with IT skills in clustering. |
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Application High Availability vs Full Virtual Machine High Availability > |
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Byte-level file replication vs block-level disk replication > |
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Virtual IP address |
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Evidian SafeKit mirror cluster with real-time file replication and failover |
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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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Uniform high availability solution > |
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Evidian SafeKit farm cluster with load balancing and failover |
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No load balancer or dedicated proxy servers or special multicast Ethernet address > |
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Remote sites and virtual IP address > |
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Uniform high availability solution > |
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This platform agnostic solution is ideal for a partner with a critical application and who wants to provide a high availability option easy to deploy to many customers.
This clustering solution is also recognized as the simplest to implement by our partners.
Server 1 (PRIM) runs the application. Clients are connected to a virtual IP address. SafeKit replicates in real time modifications made inside files through the network.
The replication is synchronous with no data loss on failure contrary to asynchronous replication.
You just have to configure the names of directories to replicate in SafeKit. There are no pre-requisites on disk organization. Directories may be located in the system disk.
When Server 1 fails, Server 2 takes over. SafeKit switches the virtual IP address and restarts the application automatically on Server 2.
The application finds the files replicated by SafeKit uptodate on Server 2. The application continues to run on Server 2 by locally modifying its files that are no longer replicated to Server 1.
The failover time is equal to the fault-detection time (30 seconds by default) plus the application start-up time.
Failback involves restarting Server 1 after fixing the problem that caused it to fail.
SafeKit automatically resynchronizes the files, updating only the files modified on Server 2 while Server 1 was halted.
Failback takes place without disturbing the application, which can continue running on Server 2.
After reintegration, the files are once again in mirror mode, as in step 1. The system is back in high-availability mode, with the application running on Server 2 and SafeKit replicating file updates to Server 1.
If the administrator wishes the application to run on Server 1, he/she can execute a "swap" command either manually at an appropriate time, or automatically through configuration.
Resynchronization time after a failure (step 3)
Alternative
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Evidian SafeKit mirror cluster with real-time file replication and failover |
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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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Uniform high availability solution > |
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Evidian SafeKit farm cluster with load balancing and failover |
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No load balancer or dedicated proxy servers or special multicast Ethernet address > |
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Remote sites and virtual IP address > |
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Uniform high availability solution > |
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Application High Availability vs Full Virtual Machine High Availability > |
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Byte-level file replication vs block-level disk replication > |
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Virtual IP address |
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