This post is intended to introduce various new ASM features introduced in Oracle Database 11g. Please find below list of the features
- New SYSASM Role for Automatic Storage Management Administration
- Disk Group Compatibility attributes
- ASM Fast Rebalance
- ASM Fast Mirror Resync
- New ASMCMD commands
- Automatic Storage Management Preferred Mirror Read
- ASM Variable size extents,scalability and performance enhancements
- Automatic Storage Management Rolling Migration
1. New SYSASM Role for Automatic Storage Management Administration
The SYSASM privilege enables the separation of the database operating system credentials from the ASM credentials.
Use the SYSASM privilege instead of the SYSDBA privilege to connect to and administer an ASM instance. If you use the SYSDBA privilege to connect to an ASM instance, then Oracle writes warnings to the alert log file because commands that you run using the SYSDBA privilege on an ASM instance will eventually be deprecated.
Oracle writes alerts to the alert log files if you issue CREATE, ALTER, or DROP DISKGOUP statements that should be performed by SYSASM.
### Alert entry ### WARNING: Deprecated privilege SYSDBA for command 'STARTUP' WARNING: Deprecated privilege SYSDBA for command 'SHUTDOWN' SQL> create diskgroup dgext external redundancy disk '/dev/raw/raw7' WARNING: Deprecated privilege SYSDBA for command 'CREATE DISKGROUP'
2. The Disk Group Compatibility feature
Two new Disk Group compatibility attributes are introduced in the Oracle 11g ASM.
The new compatible.asm and compatible.rdbms disk group compatibility attributes determine the minimum version of ASM and database instances that can connect to an ASM disk group.
Advancing the Disk group Oracle Database and ASM compatibility settings enable you to use the new ASM features that are available in the latest release. Advancing compatible.asm/compatible.rdbms attributes from 10.1 to 11.1 will enable the following key features:
– Preferred mirror read
– Variable size extents
– Fast mirror resync
The software version of ASM determines the default compatibility of newly created disk groups. You can override the disk group compatibility default setting when you create disk groups with the CREATE DISKGROUP SQL statement.
The ALTER DISKGROUP SQL statement can update the compatibility settings for existing disk groups. The compatibility settings for a disk group can only be advanced, you cannot revert to a lower compatibility setting.
Example to create diskgroup with compatible attribute :
SQL> create diskgroup dgext11gasm external redundancy disk '/dev/raw/raw7' attribute 'compatible.asm'='11.1'; Diskgroup created. SQL> create diskgroup dgext11grdbms external redundancy disk '/dev/raw/raw8' attribute 'compatible.rdbms'='11.1','compatible.asm'='11.1';
select name,compatibility,database_compatibility from v$asm_diskgroup; NAME COMPATIBILITY DATABASE_COMPATIBILITY --------- -------------------- ------------ DGEXT11GASM 18.104.22.168.0 10.1.0.0.0 DGEXT11GRDBMS 22.214.171.124.0 126.96.36.199.0
3. ASM Fast Rebalance
The RESTRICTED mode enables you to perform all maintenance tasks on a disk group in the ASM Instance without any external interaction. Rebalance operations performed while the diskgroup is in restricted mode eliminate the lock/unlock extent map messaging between ASM instances in the Oracle RAC environment, thus improving overall rebalance throughput.
Refer below post for more information about the feature.
4. ASM Fast Mirror Resync
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 or replaced.
By default, ASM drops a disk shortly after it is taken offline. You can set the DISK_REPAIR_TIME attribute to prevent this operation by specifying a time interval to repair the disk and bring it back online.
To use this feature, the disk group compatibility attributes must be set to 11.1 or higher. For more information refer below post.
5. ASMCMD New Commands
ASMCMD has the following four new commands:
The following describes the four new ASM commands:
Enables you to copy files between ASM disk groups on local instances and remote instances.
ASM can list disk information with or without a running ASM instance. This is a useful tool for system or storage administrators who want to obtain lists of disks that an ASM instance uses.
md_backup and md_restore
These commands enable you to re-create a pre-existing ASM disk group with the same disk path, disk name, failure groups, attributes, templates and alias directory structure. You can use md_backup to back up the disk group environment and use md_restore to re-create the disk group before loading from a database backup.
You can remap and recover bad blocks on an ASM disk in normal or high redundancy that have been reported by storage management tools such as disk scrubbers. ASM reads from the good copy of an ASM mirror and rewrites these blocks to an alternate location on disk.
6. Preferred Mirror Read
When ASM is managing redundancy, you can configure an ASM instance on a node to read from a preferred mirror copy (i.e. a preferred real failure group). The default behavior is to always read from the primary copy.
The feature is beneficial when you have an extended Oracle RAC cluster, where the nodes and the failure groups are separated by a long distance to enable disaster recovery. In this case, the Oracle RAC nodes on each site can be configured to read from their local storage mirror copies instead of going through a network with potentially high latencies.
The ASM_PREFERRED_READ_FAILURE_GROUPS initialization parameter to specify a list of failure group names as preferred read disks.This parameter is a multi-valued parameter and should contain a string with a list of [disk group][failure group name] separated by a comma.
7. ASM Variable size extents,scalability and performance enhancements
The variable size extent feature in Oracle Database 11g enables support for much larger ASM files, reduces SGA memory requirements for very large databases, and improves performance for file create and open functions.
An ASM file can begin with 1MB extents and as the file size increases, the extent size also increases to 8MB and 64MB at a predefined number of extents. Therefore, the size of the extent map defining a file can be smaller by a factor of 8 and 64 depending on the size of the file. The initial extent size is equal to the allocation unit size and it increases by the 8 and 64 factor at predefined thresholds.
This feature is completely automatic for newly created files once compatible.asm and compatible.rdbms have been advanced to 11.1
8. Automatic Storage Management Rolling Migration
ASM rolling upgrades enable you to independently upgrade or patch clustered ASM nodes without affecting database availability, thus providing greater uptime. Rolling upgrade means that all of the features of a clustered ASM environment function when one or more of the nodes in the cluster uses different software versions.
To perform a rolling upgrade, your environment must be prepared. If you are using Oracle Clusterware, then your Oracle Clusterware must be fully upgraded to the next patch or release version before you start the ASM rolling upgrade.In addition, you should prepare your Oracle Clusterware in a rolling upgrade manner to ensure high availability and maximum uptime.
Before you patch or upgrade the ASM software on a node, you must place the ASM cluster into rolling upgrade mode. This enables you to begin an upgrade and operate your environment in multiversion software mode. Do this by issuing the following SQL statement where number includes the version number, release number, update number, port release number, and port update number. Enter these values for number in a decimal-separated string, (e.g 188.8.131.52.0)
To perform the upgrade as in the following example:
ALTER SYSTEM START ROLLING MIGRATION TO 184.108.40.206.0;