Automatic storage management (ASM)

One could argue that ASM is not a new or unique technology. Several vendors today, such as Veritas, EMC, IBM, HP, and others, provide storage management solutions. Veritas volume manager software provides options where disks can be added to the existing volume groups. However, ASM is different because it leverages knowledge regarding datafile usage held within the Oracle RDBMS. ASM provides the capabilities of both file system and volume manager, and additionally, using the OMF hierarchical structure, it distributes I/O load across all available resources, optimizing performance.

ASM is implemented as an additional Oracle instance, which is present on each node that hosts an Oracle instance and uses the ASM facilities. ASM virtualizes the underlying disk storage: it acts as an interface between the Oracle instance and the storage devices that contain the actual data.

Here are some of the key benefits of ASM :

• I/O is spread evenly across all available disk drives to prevent hot spots and maximize performance.
• ASM eliminates the need for overprovisioning and maximizes storage resource utilization, facilitating database consolidation.
• ASM provides inherent large file support.
• Supports Oracle single-instance Database 10g, as well as RAC.
• ASM reduces Oracle Database 10g cost and complexity without compromising performance or availability.
• ASM supports mirroring of data onto different disks, providing for fault tolerance, and can be built on top of vendor-supplied reliable storage mechanisms.
• Files are created (using a standard file-naming convention) on these logical units by spreading them evenly across all disks that belong to the group.
• Disks can be added to existing disk groups dynamically without interrupting the database.
• Extents are automatically rebalanced by moving them among disks when disks are added or removed from the configuration.
• ASM integrates the OMF hierarchical structure and removes the need for file manageability.
• ASM can provide a storage management solution on single or cluster Symmetric Multiprocessor (SMP) machines.

ASM Views

ASM Dynamic Views

v$asm_alias – Lists all aliases in all currently mounted diskgroups

v$asm_client – Lists all the databases currently accessing the diskgroups

v$asm_disk – Lists all the disks discovered by the ASM instance

v$asm_diskgroup – Lists all the diskgroups discovered by the ASM instance

v$asm_file – Lists all files that belong to diskgroups mounted by the ASM instance

v$asm_operation – Reports information about current active operations.

Rebalance activity is reported in this view

v$asm_template – Lists all the templates currently mounted by the ASM instance

v$asm_diskgroup_stat – same as v$asm_diskgroup but it does discover new diskgroups. You should use this view instead of v$asm_diskgroup

v$asm_disk_stat – same as v$asm_disk but it does not discover new disks. You should use this view instead of v$asm_disk

Fixed Views

x$kfals – ASM aliases

x$kfdsk – ASM disks

x$kffil – ASM files

x$kfgrp – ASM diskgroups

x$kfgmg – ASM operations

x$kfkid – ASM disk performance

x$kfncl – ASM clients

x$kf??? – ASM templates

x$kffxp – ASM extents of ASM files relative to extents in the ASM diskgroup. Can use this view to see how well balanced individual disks are.

x$kfdat – ASM extent of diskgroup relative to extents in the ASM file