Explore Oracle's ASM concept

First,     ASM (Automated storage Management): ASM is a new feature of Oracle 10g R2 to simplify the management of Oracle databases, a volume manager delivered by Oracle itself, primarily to replace the LVM provided by the operating system. Not only does it support single instances, but it also supports the RAC very well. ASM can automate the management of disk groups and provide effective data redundancy capabilities.  www.2cto.com   using ASM (Automated storage Management), database administrators no longer need to manage and categorize hundreds of thousands of data files in Oracle, simplifying the workload of DBAs, and making them much more productive.   II.     What is ASM ASM it provides platform-independent file systems, logical volume management, and soft raid services. ASM can support stripe and disk mirroring, which enables you to add or remove disks when the database is loaded and automatically balance I/O to remove hotspots. It also supports direct and asynchronous I/O and uses the Oracle Data Manager APIs introduced in oracle9i (simplified I/O system call Interface). ASM is implemented and deployed as a separate Oracle instance, and it requires only a parameter file and no other physical file to start the ASM instance, which can be accessed by other data only when it is running. On the Linux platform, only the OCSSD service (installed by default by the Oracle installer) can be run and the ASM will be accessed.   III     use of ASM benefits: 1, the I/O average division to all available disk drives to prevent hot spots, and maximize performance. 2, more simple configuration, and maximize the use of storage resources to facilitate database consolidation. 3, the inherent support of large file 4, incremental increase or deletion of storage capacity after the automatic contact Redistribution 5, maintenance of redundant copies of data to improve availability. 6, support 10g,11g data storage and RAC shared storage Management 7, support third party multipath Software 8, use OMF way to manage files   IV     ASM redundancy: ASM uses a unique mirroring algorithm: does not mirror the disk, but the mirrored disk area. As a result, in order to provide continuous protection in the case of a failure, only the amount of space in the disk group is required, without the need to prepare a hot spare disk. Users are not recommended to create fault groups of different sizes because this will cause problems when allocating secondary extents. When ASM distinguishes a file's primary disk from a disk in a disk group, it assigns a mirrored copy of the disk to another disk in the disk group. On a given diskThe primary panel will have its own mirrored panel on one of the partner disks in the disk group. ASM ensures that the primary panel and its mirrored copies do not reside in the same failure group. The redundancy of a disk group can be in the form of common redundancy (default redundancy) for bidirectional mirrored files (at least two failed groups) and high levels of protection with a three-way mirror (requiring at least 3 failed groups).  www.2cto.com   Once you create a disk group, you cannot change its redundancy level. To change the redundancy of the disk group, you must create another disk group with appropriate redundancy, and then you must use Rman restore or Dbms_file_transfer to move the data files to this newly created disk group.   Three different redundancy methods are as follows: 1, external redundancy (external redundancy): means Oracle does not help you manage mirroring, functions are implemented by external storage systems, such as through RAID technology, and valid disk space is the size of all disk device space. 2, default redundancy (normal redundancy): Indicates that Oracle provides 2 mirrors to protect data, and that effective disk space is 1/2 of the size of all disk devices (use most) 3, highly redundant (high Redundancy): Oracle provides 3 mirrors to protect data to improve performance and data security, requiring a minimum of three disks (three failure group); The effective disk space is 1/3 of the size of all disk devices, and although the redundancy level is high, the hardware costs the most.   v     ASM Process ASM Instance In addition to the traditional Dbwr,lgwr,ckpt,smon,pmon process, the following four new background processes are included: Rbal: Responsible for coordinating disk group rebalancing activities (responsible for disk group equalization)   ARB0-ARBN: Many of these processes can exist at the same time, each named ARB0, ARB1, and so on, to perform the actual rebalancing allocation unit move process.   Gmon: For ASM disk Group monitoring   O0NN 01-10: This set of processes establishes a connection to an ASM instance, some long-running operations such as creating a data file that the RDBMS sends to ASM via these processes   ASMB and ASM An instance of the foreground process is connected to periodically check the health status of two instance. Each database instance can be connected to only one ASM instance at a time, so the database will have only one ASMB background process. If there are multiple database instances on a node, they can share only one ASM instance.   Rbal is used to make global calls to open a disk within a disk group. ASMB inProcess communicates with the CSS daemon of the node and receives the file interval mapping information from the ASM instance. ASMB is also responsible for providing I/O statistics   CSS cluster Synchronization Services for ASM instances. To use ASM, you must ensure that the CSS cluster Synchronization service is already running and that the CSS is responsible for synchronization between the ASM instance and the database instance.  www.2cto.com   NOTE: The ASM instance must be started before the database instance, synchronized with the database instance, and later closed by the database instance. The relationship between an ASM instance and a database instance can be either 1:1 or 1:n. If it is 1:n, it is a good idea to install a separate asm_home for ASM.   VI,   ASM supports automatic database file management such as Datafile,logfiles,control Files,archivelogs,rman backup sets     VII,   &NB Sp ASM instance and database instance correspondence     VIII.     Cluster ASM architecture       For more details see Oracle Database Administrator's Guide (Oracle first released): Http://docs.oracle.com/cd/B28359_01/server.111/b31107/toc.htm