Is it mandatory to use disks of same size and characteristics for Diskgroups?

No, it is not mandatory to use the disks of same size and characteristics for Diskgroups though it is a Recommended Practice.
Same size disk for Failuregroups in Normal/High redundancy will prevent issues like ORA-15041 as the file extents needs to be mirrored across the disks. Also as Oracle distributes data based on capacity, so larger disk will have more data stored in it and which will result in higher I/O to disk and eventually can lead to sub-optimal performance.
Moreover having disks of different characteristic like varying disk speed can impact the performance.
When managing disks with different size and performance capabilities, best practice is to group them into disk groups according to their characteristics. So you can use higher speed disks for your database files while other disks can be part of Diskgroup used for Flash Recovery Area.

Do we need to install ASM and Oracle Database Software in different ORACLE_HOME?

No. Again installing ASM and Oracle Database Software in different ORACLE_HOME is not mandatory but a best practice. This is useful in cases when we need to have multiple databases using same ASM instance and you need to patch only one of them. E.g You need to apply a CBO patch to one of 12.2 database while your other 12.1 database using different installation does not require it. In this case having a ASM_HOME separate from 12.2 ORACLE_HOME will allow your 12.1 database to keep running. Thus this approach is useful for High Availability.

What is the maximum size of Disk supported by ASM?

ASM supports disks upto 2Tb, so you need to ensure that lun size should be less then 2Tb. 10.2.0.4 and 11g database will give error if you try to create a diskgroup with ASM disks having disk size >2Tb.

ASM NEW FETAURES IN 12C?

Below are some fetures in 12C
1.Failgroup_repair_time
2.Online disk replace
3.Estimate Work
4.V$ASM_OPERATION view

FAILGROUP_REPAIR_TIME
For earlier ASM versions, we had disk_repair_time, from 12C onwards we have failgroup_repair_time at the ASM level. Because failure group outages are more likely to be transient in nature and because replacing all the disks in a failure group is a much more expensive operation than replacing a single disk, it would typically make sense for failure groups to have a larger repair time to ensure that all the disks do not get dropped automatically in the event of a failure group outage.

By default, the value of this diskgroup level attribute is 24Hours. To set this attribute at ASM diskgroup level, one must set compatible.asm and compatible.rdbms greater than or equal to 11.1.0.0.

Online disk replace

If an ASM disk becomes offline and cannot be repaired, administrators need the ability to replace the disk. In versions of ASM prior to 12c, there was no replace command. Rather, administrators had to drop the faulty disk and then add a new one back into the disk group which causes an ASM level rebalance. Depending on multiple internal and external factors, reblance can be time consuming.

In 12c, ASM allows DBAs to simply replace an offline disk using one fast and efficient operation. There is no need for any additional reorganization or rebalancing across the rest of the disk group. The pre-requisites for using these feature are:

1.ASM diskgroup level attribute compatible.asm should be of 12.1.0.0 for this feature
2.Replacing disk should bad in true sense , ASM will not replace online disk.
3.The replacement disk takes the same name as the original disk and becomes part of the same failure group as the original disk.
4.Then replacing good disk should be sized equal or greater than replacing bad disk.Else replace will fail.

Estimate Work
Before 12C, the only way to know how long an expensive operation like disk add/drop at diskgroup level was to actually perform the operation, so there was no way to predict before-hand how much time this would take.

In 12c ASM, a more detailed and more accurate work plan is created at the beginning of each rebalance operation. In addition, DBAs can separately generate and view the work plan before performing a rebalance operation. This allows DBA to better plan and execute various changes such as adding storage, removing storage or moving between different storage systems. DBAs can generate the work plan using the ESTIMATE WORK command.

Querying from V$ASM_ESTIMATE view give an idea of required time of that operation based on current workload on the system. This feature allows DBAs to consider system load implications while planning an operation before actually taxing the system.

Note: be sure to give the correct disk name, otherwise this estimation will fail

V$ASM_OPEARATION view
From version 11g onwards, we have a compact phase while rebalancing. While this phase used to run at ASM level for a diskgroup, we cannot estimate compact phase timing approximately.

We used to see EST_MINUTES is 0. At the same time we were also not able to track resync operations separately. In 12C, we can view these phases separately from v$asm_operation, giving a better idea about on-going operation based on current utilization of the system.

ASM NEW FETAURES IN 18C?

1.Converting Normal or High Redundancy Disk Groups to Flex Disk Groups without Restricted Mount.

You can convert a conventional disk group (disk group created before Oracle ASM 18c) to an Oracle ASM flex disk group without using the restrictive mount (MOUNTED RESTRICTED) option.

Virtual Allocation Metadata (VAM) migration must be enabled and completed before converting without the use of a restrictive mount.

2.Dropping Oracle ASM File Groups With a Cascade Option
You can drop a file group and its associated files (drop including content) using the CASCADE keyword with ALTER DISKGROUP … DROP FILEGROUP SQL statement.

3.Oracle ASM Flex Disk Group Support for Multitenant Cloning
You can create an Oracle ASM mirror clone of a multitenant database. Oracle ASM file group properties and the SQL syntax for administering pluggable databases have been updated.

4.Oracle ASM Miscellaneous Enhancements
You can set the CONTENT_HARDCHECK.ENABLED disk group attribute to enable or disable Hardware Assisted Resilient Data (HARD) checking when performing data copy operations .
The default value for the DISK_REPAIR_TIME disk group attribute has changed from 3.6 hours (3.6h) to 12 hours (12h).

5.Storage Conversion for Member Clusters
You can use ASMCMD commands to administer the configuration of member clusters. For example, you can change the storage method from direct Oracle ASM to indirect Oracle ASM, or change from indirect Oracle ASM to direct Oracle ASM.

6.Changes to ASMCMD showversion and showpatches Commands
Additional options have been provided for ASMCMD showversion and showpatches commands.

ASM NEW FEATURES IN 19C?

These are the new features for Oracle Automatic Storage Management 19c.

1.SRVCTL command enhancements
SRVCTL provides enhanced commands to manage Oracle ASM network resources.

2.Flushing the password file metadata
After a change has been made to the location of the password file, the following SQL statement should be run to flush the password file metadata cache:

sql> ALTER SYSTEM FLUSH PASSWORDFILE_METADATA_CACHE;

Changes to the location of the password file could be introduced by running orapwd, or the ASMCMD pwcopy, pwcreate, pwdelete, pwmove, or pwset command. If the V$PASSWORDFILE_INFO does not display the correct password file location after a change, then flush the password file metadata cache to force a refresh of the password file location.

3.New and updated ASMCMD commands

<>The password option with the ASMCMD pwcreate command is now optional.
New options have been added for to force a delete of the old password file and create a new password file (—f) and to specify the format of the password file (——format).

<>The new ASMCMD sets parse parent command sets the parent for a sparse child file.

<>The new ASMCMD mvfile command moves a file to the specified file group in the same disk group where the file is stored.

4.Support for Parity Protected Files
The REDUNDANCY file type property specifies the redundancy for a file group. The PARITY value specifies single parity for redundancy. The parity setting is intended for write-once files, such as archive logs and backup sets.

Do ASM has LISTENER?

Yes,just like ORACLE RDBMS ASM/Grid has LISTENER.Grid LISTENER can give service to RDBMS databases.

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