ASM learning Overview

ASM learning Overview

Oracle ASM (Oracle Automatic Storage Management)
Oracle ASM is a volume manager and a file system for Oracle database files that supports single-instance Oracle Database
And Oracle Real Application Clusters (Oracle RAC) deployments. Oracle ASM is Oracle's recommended storage management solution
That provides an alternative to conventional volume managers, file systems, and raw devices.
Oracle asm is a volume manager and a file system for Oracle database files. ASM supports single-instance and cluster configuration. It is a storage solution recommended by oracle. It is a traditional volume manager, file system, A bare device provides an option.
 
Oracle ASM uses disk groups to store data files; an Oracle ASM disk group is a collection of disks that Oracle ASM manages as a unit.
Within a disk group, Oracle ASM exposes a file system interface for Oracle database files. The content of files that are stored in a disk group is evenly distributed
To eliminate hot spots and to provide uniform performance rating ss the disks. The performance is comparable to the performance of raw devices.
Oracle ASM uses a disk group to store data files. The disk group is a collection of disks. ASM manages disks with an AU (allocate unit Allocation unit, which is 1 MB by default, but can be modified, on a disk, ASM provides a system interface for database files. The file content stored in the disk group is evenly distributed to avoid hot spots and provide balanced performance for the azimuth disk. The performance of ASM is equivalent to that of bare devices.

You can add or remove disks from a disk group while a database continues to access files from the disk group. When you add or remove disks from a disk group,
Oracle ASM automatically redistributes the file contents and eliminates the need for downtime when redistributing the content.
You can add or delete disks when using a disk group. In addition, ASM automatically resends the file content and reduces the downtime during redistribution.

Oracle ASM also uses the Oracle Managed Files (OMF) feature to simplify database file management. OMF automatically creates files in designated locations.
OMF also names files and removes them while relinquishing space when tablespaces or files are deleted.
ASM also uses OMF to simplify database file management. OMF automatically creates files at the specified location. When a tablespace or file is deleted, OMF can also name files for colleagues who release the space, delete an object.

Oracle asm ces the administrative overhead for managing database storage by using lidating data storage into a small number of disk groups.
The smaller number of disk groups extends lidates the storage for multiple databases and provides for improved I/O performance.
ASM reduces management costs by combining data to a small number of disk groups. A small number of disk groups integrate multi-database storage and provide higher I/O performance.
Oracle ASM files can coexist with other storage management options such as raw disks and third-party file systems.
This capability simplifies the integration of Oracle ASM into pre-existing environments.
The ASM instance file can coexist with other storage management devices (bare devices and third-party file systems. Capacity can simplify the integration of ASM to an existing environment.

Oracle Automatic Storage Management Cluster File System (Oracle ACFS) is a multi-platform, scalable file system, and storage management technology
That extends Oracle ASM functionality to support customer files maintained outside of Oracle Database.
The Oracle ASM Dynamic Volume Manager (Oracle ADVM) provides volume management services and a standard disk device driver interface to clients
ACFS is a multi-platform, scalable file system, storage management technology, extended ASM function to support maintenance of customer files outside the Oracle database. ADVM provides the volume Management Service and standard disk device driver interfaces for the client.

Oracle Enterprise Manager nodes des a wizard that enables you to migrate non-Oracle ASM database files to Oracle ASM.
Oracle ASM also has easy to use management interfaces such as SQL * Plus, the Oracle ASM Command Line Utility (ASMCMD) command-line interface,
Oracle ASM Configuration Assistant, and Oracle Enterprise Manager
The wizard in EM can help you migrate non-ASM database files to ASM. You can also use SQLPLUS, ASMCMD, ASMCA, and OEM.

ASM instance
An Oracle ASM instance has a System Global Area (SGA) and background processes that are similar to those of Oracle Database. However,
Because Oracle ASM performs fewer tasks than a database, an Oracle asm sga is much smaller than a database SGA. In addition,
Oracle ASM has a minimal performance effect on a server. Oracle ASM instances mount disk groups to make Oracle ASM files available to database instances;
Oracle ASM instances do not mount databases
ASM instances include SGA and some background processes. However, ASM executes fewer tasks than DB, SGA is much smaller than DB, and ASM has little impact on server performance, before starting a database instance, you must first start the ASM instance to mount the disk group. It does not mount databases.

Oracle ASM is installed in the Oracle Grid Infrastructure home before Oracle Database is installed in a separate Oracle home.
Oracle ASM and database instances require shared access to the disks in a disk group.
Oracle ASM instances manage the metadata of the disk group and provide file layout information to the database instances.
11g ASM is installed in GI home, which was previously installed in an independent oracle home. The ASM instance and the database instance access the disk. The ASM instance manages metadata in a disk group and provides file layout information for database instances. Oracle ASM metadata contains the following information:
The disks that belong to a disk group disk
The amount of space that is available in a disk group available space
The filenames of the files in a disk group file name
The location of disk group data file extended data file location
A redo log that records information about atomically changing metadata blocks changes the redo of the first data block
Oracle ADVM volume information

Oracle asm instances can use the clusteware cluster. Each node has an ASM instance. If several different database instances are on the same node, these database instances share this single asm instance. If the ASM instance fails on one node, all database instances also fail on this node. Unlike the failure of the file system driver, the ASM instance does not require OS restart, in RAC, ASM and DB instances automatically restore the fault of ASM instances on normal nodes.
In a single instance Environment, multiple database instances share one asm instance. In RAC, Oracle ASM provides a cluster storage pool, each node's ASM instance provides multiple oracle rac or single-instance DB services. All databases are merged and shared with the ASM disk group.
The Cluster Storage pool is shared by multiple single-instance databases. Multiple database instances can share a common disk group. Clustered storage pool is completed using Oracle clusterware.

Oracle ASM Disk Groups
The disk group contains multiple disks and is the basic object for managing the ASM instance. Each disk group contains metadata for space management. The disk group components include disks, files, and allocation units (AU.
Files are allocated from disks. Any ASM files are completely contained in a single disk group. However, a disk group may contain files from multiple databases, and a database may read files from multiple disk groups, for most installations, only a few disk groups are required. Generally, there are two, not more than three.

Disk Mirroring and fault Groups)
There are three methods for mirroring and three redundancy levels:
Normal for 2-way processing ing
High for 3-way processing ing
External to not use Oracle ASM flushing ing, such as when you configure hardware RAID for redundancy
The number of disk failures allowed at the redundancy level, rather than detaching the disk or losing data. The disk category determines the image level. Oracle asm images are more flexible than RAID images.
When ASM assigns an extent to an image file, oracle asm assigns a primary copy and a mirror copy. ASM selects disks to store mirror copy instead of primary copy in different fault groups.
The fault group is used to store mirror copy so that each copy is on a different fault group disk.

ASM Disk
It mainly includes the following information:
A disk or partition from a storage array
An entire disk or the partitions of a disk
Logical volumes
Network-attached files (NFS)
Description of the disk Name:
When you add a disk to a disk group, you can assign an Oracle ASM disk name or Oracle ASM assigns the Oracle ASM disk name automatically.
This name is different from the path name used by the operating system. in a cluster, a disk may be assigned different operating system device names on different nodes, but the disk has the same Oracle ASM disk name on all of the nodes. in a cluster, an Oracle ASM disk must be accessible from all of the instances that share the disk group.

Oracle ASM spreads the files proportionally stored SS all of the disks in the disk group. this allocation pattern maintains every disk at the same capacity level and ensures that all of the disks in a disk group have the same I/O load. because Oracle ASM load balances among all of the disks in a disk group, different Oracle ASM disks shoshould not share the same physical drive.

Allocation Units (AU)
Every Oracle ASM disk is divided into allocation units (AU ). an allocation unit is the fundamental unit of allocation within a disk group. A file extent consists of one or more allocation units. an Oracle ASM file consists of one or more file extents.
When you create a disk group, you can set the Oracle ASM allocation unit size with the AU_SIZE disk group attribute.
The values can be 1, 2, 4, 8, 16, 32, or 64 MB, depending on the specific disk group compatibility level.
Larger AU sizes typically provide performance advantages for data warehouse applications that use large sequential reads.

Oracle ASM Files
Files that are stored in Oracle ASM disk groups are called Oracle ASM files. Each Oracle ASM file is contained within a single Oracle ASM disk group.
Oracle Database communicates with Oracle ASM in terms of files. This is similar to the way Oracle Database uses files on any file system.
You can store the various file types in Oracle ASM disk groups, including:
Control files
Data files, temporary data files, and data file copies Data files, temporary data files, data file copy
SPFILEs server parameter file
Online redo logs, archive logs, and Flashback logs Online logs, archived logs, and Flash back logs
RMAN backups RMAN backup set
Disaster recovery ations Disaster recovery Configuration
Change tracking bitmaps
Data Pump dumpsets Data Pump File

Extended area EXTENTS
The ASM file is stored as a set of extents in the disk group, and extents is stored on different disks. Extent contains one or more AU. to accommodate larger and larger files, oracle asm uses extent of different sizes. Extent of different sizes can support larger ASM data files, reduce the memory requirements of the large database SGA, and improve the performance of File Creation and opening operations. The size of the initialized extent is equal to the size of the disk group AU, which is increased in multiples of 4 or 16.

ASM Striping (Striping)
The purpose of striping:
To balance loads internal SS all of the disks in a disk group Server Load balancer
To reduce I/O latency reduces IO latency.
To strip the data, ASM strip the file and evenly distribute the data across disks. The size of the fine strip is always kb in any configuration, provides lower IO latency.

File Templates File template
A template is a set of attribute values used to determine the disk range, file images, and striped attributes. The default template is provided to each oracle file type, but you can customize the template to meet unique requirements. Each disk group has a template associated with the file type.

ASM_DISKSTRING initialization parameters
Used to determine whether a disk group is found. For example, you can set ASM_DISKSTRING to a string with three disk groups.
Alter system set ASM_DISKSTRING = 'sys _ DG, DATA_DG, FRA_DG 'SCOPE = spfile sid =' + ASM ';

Attach and detach a disk
Alter diskgroup DATA_DG MOUNT;
Alter diskgroup DATA_DG DISMOUNT;

Online Storage Reconfigurations and Dynamic Rebalancing Online Storage reconfiguration and Dynamic Rebalancing
Rebalancing a disk group moves data between disks to ensure that every file is evenly spread internal SS all of the disks in a disk group.
When all of the files are evenly dispersed, all of the disks are evenly filled to the same percentage; this ensures load balancing.
Rebalancing does not relocate data based on I/O statistics nor is rebalancing started based on I/O statistics. Oracle ASM rebalancing operations are controlled by the size of the disks in a disk group.
ASM_POWER_LIMIT Parameter
Oracle ASM automatically initiates a rebalance after storage configuration changes, such as when you add, drop, or resize disks.
The power setting parameter determines the speed with which rebalancing operations occur.