Different sizes of ASM disks in ASM diskgroup

Reference: 

https://community.oracle.com/tech/apps-infra/discussion/4198843/different-sizes-of-asm-disks-in-asm-diskgroup

https://docs.oracle.com/cd/E11882_01/server.112/e18951/asmdiskgrps.htm#OSTMG94124

https://oracle-base.com/articles/10g/automatic-storage-management-10g

With Oracle 11.2.0.4, asmca allows me to create a diskgroup with differently sized disks, whereas asmca 12.2.0.1 does not:

 

asm11.png

 

asm3.png

 

With 12.2.0.1, it is also not possible to add a disk with a different size to an already existing disk group.

 

What works though is to replace an existing disk with a disk of a different size:

 

Connected to:Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit ProductionSQL> select name, header_status, PATH, os_mb from v$asm_disk;NAME                           HEADER_STATU PATH                           OS_MB------------------------------ ------------ ------------------------- ----------                               CANDIDATE    /dev/oracleasm/disk3g1          3072                               CANDIDATE    /dev/oracleasm/disk3g2          3072NEW1                           MEMBER       AFD:NEW1                        2048NEW2                           MEMBER       AFD:NEW2                        2048SQL> alter diskgroup NEW replace disk NEW1 with '/dev/oracleasm/disk3g1' power 11;alter diskgroup NEW replace disk NEW1 with '/dev/oracleasm/disk3g1' power 11*ERROR at line 1:ORA-15032: not all alterations performedORA-15145: ASM disk 'NEW1' is online and cannot be replaced.SQL> alter diskgroup NEW offline disk NEW1;alter diskgroup NEW offline disk NEW1*ERROR at line 1:ORA-15032: not all alterations performedORA-15283: ASM operation requires compatible.rdbms of 11.1.0.0.0 or higher(-> change compatible.rdbms )SQL> alter diskgroup NEW offline disk NEW1;Diskgroup altered.SQL> alter diskgroup NEW replace disk NEW1 with '/dev/oracleasm/disk3g1' power 11;Diskgroup altered.

 

So my takeaway is: For normal, day-to-day operation, it is a strong recommendation to have equally sized disks in a disk group. It is hard to work around that recommendation.

The ability to replace disks with larger ones exists, but If you replace disks with larger ones, it would be wise to replace all of the small disks.

As the documentation says, it is “acceptable to temporarily have disks of different sizes and performance characteristics”.

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