In the request of many netizens, this article only explains the basic concepts of the two-machine hot standby, hoping to play the role of tiles. Q: Can you explain what is a two-machine hot stand? & Nb sp; A: The so-called double-machine hot standby is to install the center server into two servers backup, and only one server is running at the same time. When the server runs in which another backup server will automatically start and run (generally 2 minutes or so), thereby ensuring the normal operation of the entire network system! The working mechanism of the double-machine hot standby is actually providing a fault automatic recovery capability for the central server of the entire network system.
Q: When is it necessary to be hot back? A: This problem is actually relatively simple, and the general server has to work for a long time, its backup work is absolutely less. Therefore, deciding whether to use a double-machine hot standby, the author will first consider the importance of the system, and the end user to take into account the tolerance of the service interrupt, and then decide whether to use the double-machine hot standby. For example, users in the network can tolerate how long to restore services? If the service can't quickly recover what consequences, etc.
Q: RAID technology and data backup technology have been taken, is it necessary to do two-machine hot backup? A: This is actually a clear distinction, RAID and data backups are equally important! Data backup can only solve the recovery after the system has problems; and RAID technology, with the author's experience, it can only solve the problem of the hard disk. We know that when the server itself has problems, whether it is the hardware problem of the device or software system, it will cause the interruption of the service, and RAID and data backup techniques do not solve the problem of avoiding service interruptions. Therefore, for high security requirements, the network system that provides application services, the two-machine hot standby is still very important. In fact, we can think about: If your server is broken, how much time you want to restore it to normal? This way you can understand the importance of double-machine hot standby!
Q: Double-standing hot spare plan and cluster difference? A: From the concept, the two-machine hot standby is one of the cluster. Clusters generally include two categories: one is a cluster of pure application servers, that is, each application server accesses unified database servers, but it does not require file sharing storage, etc., this cluster is relatively simple. Another category is a dual-hot stand for the database server. This double-machine hot standby implementation is generally two servers using shared storage devices, and in general, the main, preparation method (also high-end) The system uses a parallel way, that is, two servers simultaneously provide services).
Q: How do database services use dual-machine hot standby? A: Double-haired hot standby is achieved by software. That is, a shared storage device is not used, but the native data can flow directly between multiple hosts. Obviously, the biggest advantage of this approach is to save expensive storage equipment investment, and its shortcomings are not difficult to find: will generate data before and after, or will affect the speed of database read. Let's take a look at this example: If you switch to the backup server when the service is interrupted, there may be a small amount of transactions that have been completed in the host in the standby machine. Unlike the recovery of backup data, after the standby is started, the followed operation has been made, so the lost packet is quite difficult. Therefore, this method is suitable for systems that are not very sensitive to loss of small data.
Take a standard solution here, that is, the shared storage device and dual-machine software implement two-shelf hot standby. It provides fast switching in unattended, and does not have data loss phenomena, while investments such as storage devices will be relatively high.
