Deep analysis of two-machine hot standby scheme with pure software mode

Database dual-Machine hot equipped with two typical ways, one is more standard, two servers through a shared storage device (typically shared disk array or storage Area network SAN), and install dual-computer software, dual-machine hot standby, known as sharing mode. Another way is through a pure software approach, generally referred to as pure software or mirror mode (Mirror).

For shared methods, the database is placed on a shared storage device. When a server provides services, read and write directly on the storage device. When the system is switched, the other server also reads the data on the storage device.

For the pure software way, through the mirror software, the data can be copied to another server in real time, so the same data on both servers exist, if a server fails, you can switch to another server in time.

The pure software approach can reduce costs to some extent, but it also has very obvious drawbacks:

1. Reliability is relatively poor, real-time data replication between the two servers is a relatively weak link.

2. Once a server has been interrupted, recovery will be more complex data synchronization recovery. Also, this time period system is unprotected.

3. There is no transaction mechanism, because the replication is in the file and disk layer, the success of replication does not affect the database transaction operations, so there is a situation of incomplete data changes, there is a considerable risk.

Therefore, it is recommended that you do not choose a pure software solution unless you have to.

On the other hand, there is a kind of database parallel solution, it is not in the file or disk layer to replicate, but directly to the database operations in front of the route distribution, in parallel with the transaction mechanism to complete the update of the database, but also to provide the database of parallel services. This approach is currently very successful for SQL Server applications and is significantly better than shared storage + dual-computer software