Oracle Dual-Machine hot standby, Oracle Dataguard and Oracle RAC differences and Connections __oracle

The Data Guard is Oracle's remote replication technology, which has physical and logical points, but in general it needs to have a separate system in place, where two hardware configurations can be different, but the software structure of the two systems is consistent, including software versions, directory storage structures, As well as the data synchronization (in fact, is not real-time synchronization), the two systems as long as the network is available, is a remote disaster-tolerant solution. For RAC, it is a locally highly available cluster, where each node is used to share unused or identical applications to solve the problem of inefficient operation, single node failure, which is the same or different server for several hardware, plus a SAN (shared storage area).

The data guard consists of two more than two separate databases, each with their own storage, and Oracle is responsible for switching between them and data synchronization
Dual-Machine hot standby consists of two computers and a shared storage device, through Third-party software (HA rose, etc.) to achieve switching, do not need to do data synchronization

It is recommended that the application of Rac+dataguard, RAC ensure availability, Dataguard on a separate disk of the RAC Group and on another host, to ensure reliability.

Dual machine is what people call hot standby, the database on a shared device, the same moment can only have one host to take over, another to use, this way can only protect the instance, can not protect the DB, and standby for a long time in idle, the resources is a great waste.

If the original is a dual machine, it is recommended to convert to RAC
Planning a good application, DML operations run from one node, query operations from another node, usually do not need too much tuning can use the other idle machine

RAC servers share a single set of storage, while providing services with no primary provision. Downtime one other can continue to serve.
Dual-Machine hot standby, a shared set of storage, a service to provide a backup, the host downtime switch to the backup server to provide services.
Data Guard completely two sets of systems, the storage is separate, with log synchronization.

RAC: Instance Layer redundancy
DG: Database Layer Redundancy
Hot standby: Just data redundancy

Personal Understanding:
RAC: Instance redundancy, and can also do the loadbalance of the database.
DG: Multiple data, so you can do data redundancy, but only the main node to provide services.
Hot spare: The biggest difference with RAC may be that the RAC has multiple instances, a database. And hot standby is just an instance of a database. So I can't do concurrency and loadbalance.

Oracle RAC is only for Oracle applications, Rose,legato can also do other

HA:is the first letter combination of high availability, translated, can be called highly available, or high availability, high availability (environment). I think it should be said that HA is an idea, not a single or a series of specific techniques, like grids. Once the system scheme is known, there is a high availability of evaluation system performance. The broad sense of high availability involves all aspects of the system, simply, so that the system does not interrupt the operation, is highly available. Including high availability of software, high availability of hardware, high availability of the network, and so on. The implementation of the program includes the operating system cluster, database cluster, hardware redundancy, network redundancy and so on. To do ha software, there are IBM's HACMP (many commonly used AIX people, often said Ha refers to hacmp, chaos), Sun Sun Cluster, HP Mc/sg and so on.

Before 2000, we talk about Ha, most of the time is the operating system level of dual-machine hot standby, mainstream products at that time IBM HACMP4.1,HP MC/SG What version of the Forgotten, sun system Many people do not use the VCS, with a call dataware things. Ha is still the same in many people's eyes now. Today, Ha includes a lot of things, not to mention other aspects, single database, Oracle, HA-related products successively: Advanced Replication (Advancerepication), Ops/rac (real application Cluster), Several products such as data Guard, Oracle Streaming (Oracle Streams), partitioning (Oracle Partition). In that case, RAC is just a specific product of the HA concept. So far, only the RAC and partitions are Oracle to charge licence, others, as long as the experienced Third-party implementation to pay a certain planning/design and deployment costs can be, of course, you can follow the document according to the gourd, but the environment can be achieved high availability is hard to say. In fact, most people say that ha, or the narrow sense of ha, that is, OS-level dual-machine hot standby.

RAC:is the short name of real application cluster, which is the technique of running a database on multiple hosts, that is, a DB multiple instance. The advantage of this is that it can be built by a number of poor performance of a cluster of good performance, and achieve load balancing, then when a node failure, the service will automatically go to another node to execute, the user does not even feel anything.

What is the difference between hot standby (HA) and RAC?

1, for the hardware, basically, shared storage, fiber-optic cables (also with SCSI lines), multiple small machines (which can be hot-standby for a long node, or a RAC with more nodes), fiber-optic switches (if the fiber card is used); but do RAC, between hosts, It is best to use High-bandwidth network switches (although they can not be made), so there is little difference in hardware costs.
2, software, the difference is not small. If it is a dual-machine hot standby, you must buy the operating system-level dual-Computer management software; If it is RAC, it is still recommended to buy dual-Computer Management software (although 10g crs+asm can get rid of dual-computer software, but ASM is too difficult to serve), of course, have to buy RAC license
3, daily maintenance. RAC requires a higher level of technology and should be more diligent. The key is to buy Oracle services, otherwise there are some problems (bugs), you are not higher than the single machine is available.
4. Advantages and disadvantages. This, look at the official discussion of RAC. If we can use it well, it is really good. At present, the use of our more than 40 customers, RAC does greatly reduce their downtime, on the other hand, can be said to improve productivity slightly.

Dataguard:It is generally for disaster-tolerant purposes. is the primary database's standby library (standby library) by automatic transfer and acceptance of Archivelog, and automatically apply these logs in the Dataguard library to achieve synchronization with the main database, May Dataguard library is built offsite, When there is a fatal disaster in the area where the main library is located (fire, earthquake, etc.), the main library can not be repaired, at which point the Dataguard is switched to the main library mode to provide services externally, and its data is basically current. At present, the use of Dataguard library may have been extended to other uses, such as backup, running reports and so on.

Track data:http://blog.csdn.net/graemes/article/details/6192185