What are the 4 states of a database

Oracle10g database 4 kinds of storage forms

The existence of the database must need to have a permanent storage method and media.Oracle is naturally no exception.In Oracle10g,there are 4 kinds of storage forms,respectively,operating system files,bare partitions,automatic storage management,cluster system OCFS(RAC). The following is a description of each of these four forms of storage.1 Operating system files. This is the most commonly used way, but also non-commercial mode of operation (such as development or development phase of the test environment) under the most commonly used form. When you install Oracle, if you choose the operating system file storage form, then the Oracle data will be stored in the operating system, in the form of files. It's like when we play some single-player game, your archive is the operating system file. Storing data in file form brings the advantage of easy database movement. For example, you copy the Oracle data files directly to a computer, you can quickly copy a database system out of the same. In the file read and write, the operating system will usually provide a cache form of read and write, to avoid too much read and write hard disk on the disk to cause great harm. So storing data in the form of operating system files is the same as innately obtaining the caching function of the operating system.

2 Bare partitioning. Bare partition is to write the database directly on the disk, no longer after the operating system layer, Oracle specializes in reading and writing to this partition. Because there is no operating system layer, so read and write up the speed and performance is the general quality of the leap in some of the Oracle read and write very frequently in the database application, the use of bare partition form of data storage can even improve the performance of more than 30%. Of course, if the data storage is used in the operating system files, if the Unix RAID is used in the case of frequent file read and write operations is also a means to improve performance.

3 Automatic storage management. Automatic Storage Management, also commonly referred to as ASM, is a new form of storage that has been available since Oracle 10g. This form of storage appears to be a compromise between the first two forms of storage. Neither the file system of the host operating system is used, nor is it in the form of bare partitions that are read or written to directly by Oracle. Rather, it can be seen as a form of Oracle-specific file system. In the ASM can store data files, control files, log files, etc., in the ASM, these are also in the form of files exist, but this time the file format is Oracle's own ASM form. In Linux and ASM is somewhat similar to the LVM (Logical Volume Management), can also be seen as a new form of its own file system.

4 Clustered system OCFS (RAC). what is the full name of the RAC is Real Application Cluster, is a kind of clustered environment to achieve **** enjoy a form of database storage. In general, our database, if it is a stand-alone version of the database, when the data file disk can not be accessed, then the database hangs. If it is a cluster *** enjoy the database, one of the methods is to store the data file in a node, the rest of the database through NFS or Samba to *** enjoy, although the database data processing capacity has been greatly improved, but if the storage node hangs, the same database will be down. OCFS is a form of storage without breakpoint recovery, in the overall feeling is that each data server has its own file system, but these file systems seem to be just the same file system, because the data update or other operations are very uniform. Even if a computer hangs, the rest of the servers are still running, there will be no database anomaly, and if you want to add a new server is also a very simple thing. Especially suitable for commercial 7X24 this form of service.

Oracle10g in the four kinds of data storage are introduced, we most commonly used is the first form of nature, but the latter three forms in the commercial environment more. Especially in the large commercial to go to the reliability of very high applications, the fourth RAC form of use is more. Of course, here is only a very brief introduction to a few file system concepts. If you want to know more about it, of course, you need to consult the Oracle technical manuals.