Automated Storage Systems (ASM) in Oracle

First, ASM (Automatic storage management) for the reason:

ASM is a new feature introduced in Oracle 10g R2 to simplify the management of Oracle databases, a volume manager provided by Oracle itself, primarily used to replace the LVM provided by the operating system, which not only supports single instancing, but also supports the RAC very well. ASM can automatically manage disk groups and provide effective data redundancy capabilities. With ASM (Automatic storage Management), database administrators no longer need to manage and categorize thousands of data files in Oracle, simplifying the workload of DBAs and making productivity much more productive.

Second, what is ASM

ASM it provides platform-independent file systems, logical volume management, and soft raid services. ASM supports stripe and disk mirroring, enabling you to add or remove disks and automatically balance I/O when the database is loaded to remove hotspots. It also supports direct and asynchronous I/O and uses the Oracle Data Manager API (simplified I/O system invocation Interface) introduced in Oracle9i.

ASM is implemented and deployed as a separate Oracle instance, and it only needs to have parameter files, no other physical files, to launch an ASM instance that can be accessed by other data only when it is running. On the Linux platform, only the OCSSD service (the Oracle installer is installed by default) can be run and access ASM.

III. Benefits of using ASM:

1. Averaging the I/O to all available disk drives to prevent hotspots from being generated and maximizing performance.

2, the configuration is more simple, and maximize the use of storage resources to promote database consolidation.

3. Supporting large files within

4. Perform automatic contact redistribution after incremental or delete storage capacity

5. Maintain redundant copies of data to improve availability.

6. Support 10G,11G data storage and RAC shared storage management

7. Support for third-party multi-Path software

8. Use OMF mode to manage files

Iv. ASM Redundancy:

ASM uses a unique mirroring algorithm: it does not mirror disks, but mirrors the extents. As a result, in order to provide continuous protection in the case of a failure, only the space capacity in the disk group is required, without the need to prepare a hot spare disk. It is not recommended that users create fault groups of different sizes, as this will cause problems when assigning secondary extents. ASM assigns a primary disk of a file to a disk in a disk group, which allocates a mirrored copy of that region to another disk in the disk group. The primary extents on a given disk will have their own mirrored extents on one of the partner disks in the disk group. ASM ensures that the primary extents and their mirrored copies do not reside in the same fault group. the redundancy of a disk group can be as follows: Normal redundancy (default redundancy) for bidirectional image files (with a minimum of two fault groups) and high redundancy with a three-way mirror (requiring at least 3 fault groups) for a higher degree of protection. 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 the appropriate redundancy, and then you must use Rman restore or Dbms_file_transfer to move the data files to the newly created disk group.

The three different redundancy methods are as follows:

1, external redundancy (external redundancy): means that Oracle does not manage the image for you, functions are implemented by an external storage system, such as through RAID technology; effective disk space is the sum of the size of all disk device space.

2. default redundancy (normal redundancy): indicates Oracle provides 2 images to protect data, valid disk space is 1/2 of the sum of all disk device sizes (most used)

3. highly redundant (high redundancy): indicates that Oracle provides 3 images to protect data to improve performance and data security, requires a minimum of three disks (three failure group), and valid disk space is 1 of the sum of all disk device sizes 3, although the redundancy level is high, the hardware is the most expensive.

V. ASM PROCESS

ASM examples include the following four new background processes in addition to the traditional Dbwr,lgwr,ckpt,smon,pmon process:

Rbal: responsible for coordinating disk group rebalancing activities (responsible for disk group equalization)

ARB0-ARBN: There can be many such processes at the same time, each named ARB0, ARB1, and so on, performing 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, and some long-time operations such as creating a data file, the RDBMS sends information to ASM through these processes

ASMB is connected to the foreground process of the ASM instance, periodically checking the health status of two instance. Each DB instance can be connected to only one ASM instance at a time, so the database will only have one ASMB background process. If there are multiple DB instances on a node, they can share only one ASM instance.

The Rbal is used to make a global call to open a disk in a disk group. The ASMB process communicates with the node's CSS daemon and receives the file interval mapping information from the ASM instance. ASMB is also responsible for providing I/O statistics for ASM instances

CSS cluster Synchronization service. To use ASM, you must ensure that the CSS Cluster Synchronization service is running and that the CSS is responsible for synchronizing between the ASM instance and the DB instance.

Note: An ASM instance must be started before the DB instance and run synchronously with the DB instance later than the DB instance is closed. The relationship between an ASM instance and a DB instance can be either 1:1 or 1:n. If it is 1:n, it is best 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

Seven, ASM instance and DB instance correspondence relationship

Automated Storage Systems (ASM) in Oracle