【 Weak current College 】 database in standby machine software summary of benefits

Hot standby database is the database users need to consider the importance of data security is never chant ignored. A good two-computer backup for the database to provide a good storage environment.

Database two typical hot available, one is more standard, two servers through a shared storage device (typically shared disk array or storage area network SAN), and the installation of computer software, hot standby database, known as shared methods. Another way is by pure software, commonly known as a pure software or mirror (Mirror).

For shared mode, the database on a shared storage device. When a server providing services, directly on a storage device for read and write. But when the system is switched to another server to also read the data on the storage device.

For pure software, by way of data mirroring software, can real-time replication to another server, so the same data as in the two exist on one server, if one server fails, you can promptly switched to another server.

Pure software has three main advantages:

1. avoiding disk arrays of single points of failure: hot standby for the database itself that is prevention because a single device fault cause service disruptions, but disk array exactly and formed a new single-point. (For example, the server's reliability coefficient is 99.9% disk array of reliable coefficient is 99.95% pure soft double machine reliability coefficient is 1-99.9% x99.9% = 99.99%, while the database based on RAID hot standby system reliability coefficient will be slightly lower than 99.95%

2. save investment: does not require expensive disk array.

3. no distance limitation: two servers do not need to be SCSI cable length limit (Fibre Channel disk arrays are not affected by distance limitations, but the investment will be much more). This allows more flexibility in deploying servers, including through the physical location of the distance to improve security.

Pure software previously applied less, partly because of the more popular on the market at that time two-machine software does not support pure software, on the other hand is due to how a minority support pure software products whose reliability is not very reassuring. But as Lifekeeper such high card manufacturers of products entering the market, it should be said that pure software will gradually become a trend.

Choose from a programme, recommends the angle of the standby database, if the investment is sufficient, the amount of data (1T), you can use shared storage device (such as a disk array), but should try to select high reliability (such as the famous brand of) device. Otherwise, the better choice is a pure software. Of course, be sure to select the mature, large manufacturers of the products tested.

Database-standby, dual machine preparation and double machine each duplex difference

Hot standby database is now commonly referred to as active/standby mode, the server data includes database data simultaneously to two or more servers, or use a shared storage device. When the active Server fails, the log through software consultation (typically by heartbeat Diagnostics) to activate the standby machine, ensure that application in a short time to completely back to normal use.

Double Cross, in the standby database on the basis of two relatively independent of the application on two machines running at the same time, but they are set to backup machine, when a server fails, another server can in a short period of time, the application of the failed server to take over, thus ensuring the sustainability of the application. In this way is actually a hot standby. It avoids two application uses four servers are hot standby database.

Double duplex, two or more servers are active, while running the same application, ensure that the overall performance, but also implements load balancing and backup each other. There is a need to use disk cabinet storage technology (preferably a San). For database services, it also requires a database software support, is more complex. While the WEB server or application server is relatively simple.