Automatic Storage Management (ASM) is a feature provided by

Oracle Corporation Oracle Corporation is an American multinational computer technology corporation headquartered in Austin, Texas. In 2020, Oracle was the third-largest software company in the world by revenue and market capitalization. The company sells da ...

within the

Oracle Database Oracle Database (commonly referred to as Oracle DBMS, Oracle Autonomous Database, or simply as Oracle) is a multi-model database management system produced and marketed by Oracle Corporation. It is a database commonly used for running online ...

from release Oracle 10g (revision 1) onwards. ASM aims to simplify the management of

database In computing, a database is an organized collection of data stored and accessed electronically. Small databases can be stored on a file system, while large databases are hosted on computer clusters or cloud storage. The design of databases spa ...

datafiles, control files and log files. To do so, it provides tools to manage

file system In computing, file system or filesystem (often abbreviated to fs) is a method and data structure that the operating system uses to control how data is stored and retrieved. Without a file system, data placed in a storage medium would be one lar ...

s and

volume Volume is a measure of occupied three-dimensional space. It is often quantified numerically using SI derived units (such as the cubic metre and litre) or by various imperial or US customary units (such as the gallon, quart, cubic inch). Th ...

s directly inside the database, allowing

database administrator Database administrators (DBAs) use specialized software to store and organize data. The role may include capacity planning, installation, configuration Configuration or configurations may refer to: Computing * Computer configuration or system c ...

s (DBAs) to control volumes and disks with familiar SQL statements in standard Oracle environments. Thus DBAs do not need extra skills in specific

s or volume managers (which usually operate at the level of the

operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ef ...

Features

* IO channels can take advantage of

data striping In computer data storage, data striping is the technique of segmenting logically sequential data, such as a file, so that consecutive segments are stored on different physical storage devices. Striping is useful when a processing device reques ...

and software

mirroring Mirroring is the behavior in which one person subconsciously imitates the gesture, speech pattern, or attitude of another. Mirroring often occurs in social situations, particularly in the company of close friends or family, often going unnoticed ...

* DBAs can automate online redistribution of data, along with the addition and removal of disks/storage * the system maintains redundant copies and provides 3rd-party

RAID Raid, RAID or Raids may refer to: Attack * Raid (military), a sudden attack behind the enemy's lines without the intention of holding ground * Corporate raid, a type of hostile takeover in business * Panty raid, a prankish raid by male colleg ...

functionality * Oracle supports third-party multipathing IO technologies (such as

failover Failover is switching to a redundant or standby computer server, system, hardware component or network upon the failure or abnormal termination of the previously active application, server, system, hardware component, or network in a computer n ...

or load balancing to SAN access) * the need for

hot spare A hot spare or warm spare or hot standby is used as a failover mechanism to provide reliability in system configurations. The hot spare is active and connected as part of a working system. When a key component fails, the hot spare is switched ...

s diminish

Architecture overview

ASM creates

extent Extent may refer to: Computing * Extent (file systems), a contiguous region of computer storage medium reserved for a file * Extent File System, a discontinued file system implementation named after the contiguous region * Extent, a chunk of st ...

s out of datafiles, log-files, system files, control files and other database structures. The system then spreads these extents across all disks in a "diskgroup". One can think of a diskgroup in ASM as a

Logical Volume Manager In computer storage, logical volume management or LVM provides a method of allocating space on mass-storage devices that is more flexible than conventional partitioning schemes to store volumes. In particular, a volume manager can concatenate, ...

volume group In Linux, Logical Volume Manager (LVM) is a device mapper framework that provides logical volume management for the Linux kernel. Most modern Linux distributions are LVM-aware to the point of being able to have their root file system I ...

— with an ASM file corresponding to a

logical volume In computer storage, logical volume management or LVM provides a method of allocating space on mass-storage devices that is more flexible than conventional partitioning schemes to store volumes. In particular, a volume manager can concatenate, ...

. In addition to the existing Oracle

background process A background process is a computer process that runs ''behind the scenes'' (i.e., in the background) and without user intervention. Typical tasks for these processes include logging, system monitoring, scheduling, and user notification. The backgr ...

es, ASM introduces two new ones - OSMB and RBAL. OSMB opens and creates disks in a diskgroup. RBAL provides the functionality of moving data between disks in a diskgroup.

Implementation and usage

Automatic Storage Management (ASM) simplifies administration of Oracle-related files by allowing the administrator to reference disk groups (rather than individual disks and files) which ASM manages. ASM extends the Oracle Managed Files (OMF) functionality that also includes striping and mirroring to provide balanced and secure storage. DBAs can use the ASM functionality in combination with existing raw and cooked file-systems, along with OMF and manually managed files. An ASM ''instance'' controls the ASM functionality. It isn't a full database instance, it provides just the memory structures, and as such is very small and lightweight. The main components of ASM are disk groups, each of which comprise several physical disks controlled as a single unit. The physical disks are known as ASM disks, while the files that reside on the disks are known as ASM files. The locations and names for the files are controlled by ASM, but user-friendly aliases and directory structures can be defined by the DBA for ease of reference. The level of redundancy and the granularity of the striping can be controlled using templates. Oracle Corporation provides default templates for each file-type stored by ASM, but additional templates can be defined as needed. Failure groups are defined within a disk group to support the required level of redundancy. For two-way mirroring, a disk group might contain two failure groups, in which case individual files are written to two locations. Oracle ASM Dynamic Volume Manager provides the foundation for the ASM Cluster File System (ACFS). In summary, ASM provides the following functionality: * manages groups of disks, called disk groups * manages disk redundancy within each disk group * provides near-optimal I/O balancing without any manual tuning * enables management of database objects without specifying mount-points or filenames * supports large files

Redundancy

One can configure ASM diskgroups to have no redundancy (external), two-way mirroring (normal), or three-way mirroring (high). In the case of normal and high mirrors, good practice suggests having fail groups that talk to different controllers for performance and fail-safe reasons. * In the case of external redundancy, ASM does not do any software mirroring, but only stripes its files across all the disks that belong to the disk group that does external redundancy. * In the case of normal redundancy, ASM does two-way mirroring, meaning that ASM maintains two copies of the data through software mirroring. When querying for mirror information, DBAs will see two mirrors in this case. * In the case of high redundancy, ASM does three-way mirroring, maintaining three copies of the data through software mirroring. When querying for mirror information, DBAs will see three mirrors in this case.

References

{{reflist

External links