How to create diskgroup in ASM?

CREATE DISKGROUP disk_group_2 EXTERNAL REDUNDANCY DISK '/dev/sde1';

If want to mentioned the failgroup use below command.

CREATE DISKGROUP disk_group_1 NORMAL REDUNDANCY
  FAILGROUP failure_group_1 DISK
    '/devices/diska1' NAME diska1,
    '/devices/diska2' NAME diska2
  FAILGROUP failure_group_2 DISK
    '/devices/diskb1' NAME diskb1,
    '/devices/diskb2' NAME diskb2;

How to drop diskgroup in ASM?

DROP DISKGROUP disk_group_1 INCLUDING CONTENTS;

How to resize ASM disk in diskgroup?

-- Resize a specific disk.
ALTER DISKGROUP disk_group_1
  RESIZE DISK diska1 SIZE 100G;

-- Resize all disks in a failure group.
ALTER DISKGROUP disk_group_1
  RESIZE DISKS IN FAILGROUP failure_group_1 SIZE 100G;

-- Resize all disks in a disk group.
ALTER DISKGROUP disk_group_1
  RESIZE ALL SIZE 100G;

How to MOUNT or DISMOUNT diskgroups manually?

ALTER DISKGROUP ALL DISMOUNT;
ALTER DISKGROUP ALL MOUNT;
ALTER DISKGROUP disk_group_1 DISMOUNT;
ALTER DISKGROUP disk_group_1 MOUNT;

What is stripping and mirroring?

Striping is spreading data across multiple disks so that IO is spread across multiple disks and hence increase in throughput. It provides read/write performance but fail over support.
ASM offers two types of striping, with the choice depending on the type of database file. Coarse striping uses a stripe size of 1MB, and you can use coarse striping for every file in your database, except for the control files, online redo log files, and flashback files. Fine striping uses a stripe size of 128KB. You can use fine striping for control files, online redo log files, and flashback files.

Mirroring means redundancy. It may add performance benefit for read operations but overhead for write operations. It’s basic purpose is to provide fail over support.
There are three ASM mirroring options:

High Redundancy – In this configuration, for each primary extent, there are two mirrored extents. For Oracle Database Appliance this means, during normal operations there would be three extents (one primary and two secondary) containing the same data, thus providing “high” level of protection. Since ASM distributes the partnering extents in a way that prevents all extents to be unable due to a component failure in the IO path, this configuration can sustain at least two simultaneous disk failures on Oracle Database Appliance (which should be rare but is possible).

Normal Redundancy – In this configuration, for each primary extent, there is one mirrored (secondary) extent. This configuration protects against at least one disk failure. Note that in the event a disk fails in this configuration, although there is typically no outage or data loss, the system operates in a vulnerable state, should a second disk fail while the old failed disk replacement has not completed. Many Oracle Database Appliance customers thus prefer the High Redundancy configuration to mitigate the lack of additional protection during this time.

External Redundancy – In this configuration there are only primary extents and no mirrored extents. This option is typically used in traditional non-appliance environments when the storage sub-system may have existing redundancy such as hardware mirroring or other types of third-party mirroring in place. Oracle Database Appliance does not support External Redundancy.8. What is a diskgroup?
A disk group consists of multiple disks and is the fundamental object that ASM manages. Each disk group contains the metadata that is required for the management of space in the disk group. The ASM instance manages the metadata about the files in a Disk Group in the same way that a file system manages metadata about its files. However, the vast majority of I/O operations do not pass through the ASM instance. In a moment we will look at how file I/O works with respect to the ASM instance.

What is ASM Rebalancing ? When rebalancing occurs?

ASM REBALANCING. Dynamic Storage Configuration. ASM enables you to change the storage configuration without having to take the database offline. It automatically rebalances/redistributes file data evenly across all the disks of the disk groups. Rebalancing occurs when we add disks to or drop disks from a disk group.

How to check rebalancing is in progress or estimated time for rebalancing to complete ?

select * from   V$ASM_OPERATION ;

How does this filesystem structure appear?

Oracle ASM disk group’s filesystem structure is similar to UNIX filesystem hierarchy or Windows filesystem hierarchy.

Where are the Oracle ASM files stored?

Oracle ASM files are stored within the Oracle ASM diskgroup. If we dig into internals, oracle ASM files are stored within the Oracle ASM filesystem structures.

What are the Oracle files that are stored within the Oracle ASM file hierarchy?

Files stored in Oracle ASM diskgroup/Oracle ASM file structures include:
1) Datafile
2) Controlfiles
3) Server Parameter Files(SPFILE)
4) Redo Log files 5) Archives logfiles

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