Oracle ASM 18c - Features

 

18c Database : ASM DISK Groups Enhancements

In this post, we will see few important ASM Disk group Level Enhancements in 18c.

DISK_REPAIR_TIME : Increased from 3.5 hrs to 12 Hrs

When a disk is taken offline from a disk group , the diskgroup will not immediately dropped as it waits for 3.5 Hrs as DISK_REPAIR_TIME , but now that is changed to 12 Hrs. Until then Oracle ASM fast resync keeps track of pending changes to extents on an offline disk during an outage. The extents are resynced when the disk is brought back online.

 

FLEX Disk Groups : Convert a normal diskgroup to flex diskgroup without diskgroup mount restricted.

In 12cR2, Oracle introduced Flex Disk group to have more granularity at Database level usage of storage, by segregating the storage into file groups etc. The disk group can be converted from normal to flex diskgroup and then add a filegroups with for each diskgroup.  So to convert a normal diskgroup to a flex diskgroup the disk group must be in mount restricted mode.

In 18c, the mount restricted is not required for conversion you can convert the diskgroup from normal to flex diskgroup online.

Create a flex diskgroup
CREATE DISKGROUP flex_data FLEX REDUNDANCY DISK my_disk_discovery_path;
Diskgroup created.

Create a normal diskgroup
CREATE DISKGROUP normaltoflex NORMAL REDUNDANCY DISK '/devices/diskm*' ATTRIBUTE 'au_size'='4M', 'compatible.asm' = '18.0', 'compatible.rdbms' = '18.0','compatible.advm' = '18.0';
Diskgroup created.

Convert from Normal to Flex diskgroup
ALTER DISKGROUP normaltoflex CONVERT REDUNDANCY TO FLEX;

 

File Groups : Drop with cascade option

You can drop a file group including its associated files (drop including content) using the CASCADE keyword with the ALTER DISKGROUP ... DROP FILEGROUP SQL statement or the —r option with the ASMCMD rmfg command.

ALTER DISKGROUP DiskGroup_1 DROP FILEGROUP TEST CASCADE;

-Thanks

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

I have a NORMAL REDUNDANCY disk group named DG_FLEX. I will convert this DG to FLEX redundancy to demonstrate this new feature

Note: To Convert the diskgroup to FLEX redundancy without mounting it in restricted mode
Following is required

1) ASM Version 18c
2) 'compatible.asm' = '18.0.0.0.0';
3) 'compatible.advm'='18.0.0.0.0';
4) 'compatible.rdbms'='12.2.0.0.0' or higher;
5) 'VAM_MIGRATION_DONE'='true'

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

You can set the DG attributes of a disk group as shown below

SQL> ALTER DISKGROUP DG_FLEX SET ATTRIBUTE 'compatible.asm' = '18.0.0.0.0';

Diskgroup altered.

SQL> ALTER DISKGROUP DG_FLEX SET ATTRIBUTE 'compatible.advm'='18.0.0.0.0';

Diskgroup altered.

SQL> ALTER DISKGROUP DG_FLEX SET ATTRIBUTE 'compatible.rdbms'='18.0.0.0.0';

Diskgroup altered.

SQL> ALTER DISKGROUP DG_FLEX SET ATTRIBUTE  'VAM_MIGRATION_DONE'='true';

Diskgroup altered.

SQL> select DG.NAME,DG.STATE,DG.TYPE as REDUNDANCY,DS.STATE,DS.MODE_STATUS,DS.HEADER_STATUS,DS.MOUNT_STATUS,DS.NAME from v$asm_diskgroup dg,v$asm_disk ds where dg.GROUP_NUMBER=ds.GROUP_NUMBER and DG.NAME='DG_FLEX';

NAME                           STATE       REDUNDANCY STATE    MODE_ST HEADER_STATU MOUNT_S NAME
------------------------------ ----------- ---------- -------- ------- ------------ ------- -------------------
DG_FLEX                        MOUNTED     NORMAL     NORMAL   ONLINE  MEMBER       CACHED  FLEX_DATA02
DG_FLEX                        MOUNTED     NORMAL     NORMAL   ONLINE  MEMBER       CACHED  FLEX_DATA03
DG_FLEX                        MOUNTED     NORMAL     NORMAL   ONLINE  MEMBER       CACHED  FLEX_DATA01

SQL>  ALTER DISKGROUP DG_FLEX CONVERT REDUNDANCY TO FLEX;
Diskgroup altered.

SQL> select DG.NAME,DG.STATE,DG.TYPE as REDUNDANCY,DS.STATE,DS.MODE_STATUS,DS.HEADER_STATUS,DS.MOUNT_STATUS,DS.NAME from v$asm_diskgroup dg,v$asm_disk ds where dg.GROUP_NUMBER=ds.GROUP_NUMBER and DG.NAME='DG_FLEX';

NAME                           STATE       REDUNDANCY STATE    MODE_ST HEADER_STATU MOUNT_S NAME
------------------------------ ----------- ---------- -------- ------- ------------ ------- -------------------
DG_FLEX                        MOUNTED     FLEX       NORMAL   ONLINE  MEMBER       CACHED  FLEX_DATA02
DG_FLEX                        MOUNTED     FLEX       NORMAL   ONLINE  MEMBER       CACHED  FLEX_DATA03
DG_FLEX                        MOUNTED     FLEX       NORMAL   ONLINE  MEMBER       CACHED  FLEX_DATA01

Dropping Oracle ASM File Groups With a Cascade Option

starting with 18c you can drop a file group with Cascade option. This will drop all the associated files including content with this file group and you no longer need to manually cleanup them up.

SQL> ALTER DISKGROUP DG_FLEX DROP FILEGROUP FG_PDB1 CASCADE;
Diskgroup altered.

Point-In-Time Database Cloning With Oracle ASM Flex Disk Groups

Oracle ASM provides support for creating a point-in-time database clone which is a

mirror copy of a pluggable database. All the data files of the database being cloned
should be present in a single disk group. The cloning operation can be used for rapid
provisioning of identical copies. You can specify the redundancy setting of the
database data files in the database clone, or the setting can default to the redundancy
of the data files in the source database that is being the cloned. The Point in time cloning is done using following steps.

Step1- Preparing the Mirrored Copy
Step2- Splitting the Mirrored Copy and Creating the Database Clone
Step3- Dropping the Prepared Mirror Copy

Detailed technical steps of this topic is not part of this post and will be covered in a separate post