Applies to:
Oracle Database - Enterprise Edition - Version 11.1.0.6 to 11.1.0.6 [Release 11.1]
Linux x86
Purpose
This document is intended to introduce various new ASM features introduced in Oracle Database 11g.
Please find below list of the features
1) New SYSASM Role for Automatic Storage Management Administration
2) Disk Group Compatibility attributes
3) ASM Fast Rebalance
4) ASM Fast Mirror Resync
5) New ASMCMD commands
6) Automatic Storage Management Preferred Mirror Read
7) ASM Variable size extents,scalability and performance enhancements
8) Automatic Storage Management Rolling Migration
Scope
All the DBAs and users concerned with Database Administration activities.
Details
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.
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 enables you to use the new ASM features that are available in 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.
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 11.1.0.0.0 10.1.0.0.0
DGEXT11GRDBMS 11.1.0.0.0 11.1.0.0.0
Note.433710.1 - ORA-15234 target RDBMS compatibility (11.1.0.0.0) exceeds ASM compatibility
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 Oracle RAC environment, thus improving overall rebalance throughput.
Refer below note for more information about the feature
Note 445037.1 - ASM Fast Rebalance
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 Note
Note.443835.1 - ASM Fast Mirror Resync - Example to simulate transient disk failure and restore disk
5.ASMCMD New Commands
ASMCMD has the following four new commands: lsdsk,md_backup,md_restore and remap
The following describes the four new ASM commands:
group environment and use md_restore to re-create the disk group before loading from a database backup.
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(ie a preferred real failure group). The default behaviour 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 seperated 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 newtwork 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> seperated 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 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 advance 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 11.2.0.0.0)
To perform the upgrade as in the following example
ALTER SYSTEM START ROLLING MIGRATION TO 11.2.0.0.0;
References
NOTE:433710.1 -
ORA-15234: Target RDBMS Compatibility (11.1.0.0.0) Exceeds ASM Compatibility
NOTE:445037.1 -
ASM Fast Rebalance
ASM Fast Rebalance [ID 445037.1]
Applies to:
Oracle Server - Enterprise Edition - Version: 11.1.0.6 to 11.1.0.6 - Release: 11.1 to 11.1
Information in this document applies to any platform.
***Checked for relevance on 27-Feb-2011***
Purpose
This article talks about the 11g new feature - ASM Fast rebalance and how to implement in 11g ASM Instance
Scope and Application
All DBA's and user's concerned with Database and ASM Administration activities.
ASM Fast Rebalance
ASM Fast Rebalance
In 11g, you can use the STARTUP RESTRICT command to control access to an ASM instance while you perform maintenance. This startup option is used to implement ASM
Fast Rebalance feature. Rebalance operations that occur while a disk group is in RESTRICTED mode eliminate the lock and unlock extent map messaging between ASM instances in
Oracle RAC environments.
When an ASM instance is started with 'STARTUP RESTRICT' option and is active in this mode, all of the disk groups are mounted in RESTRICTED mode which prevents databases from connecting
to the ASM instance. In addition, the restricted clause of the ALTER SYSTEM statement is disabled for the ASM instance.
Given below is an example to show ASM Fast Rebalance Feature.
Startup ASM instance in Restricted mode
SQL> startup restrict;
ASM instance started
Total System Global Area 92065792 bytes
Fixed Size 1297984 bytes
Variable Size 65601984 bytes
ASM Cache 25165824 bytes
Now in case you wish to mount the Disk group in normal mode , you get following errors
SQL> alter diskgroup dgext11gasm mount;
alter diskgroup dgext11gasm mount
*
ERROR at line 1:
ORA-15251: only restricted mount is allowed in the ASM instance
You need to use restricted clause along with mount option.
SQL> alter diskgroup dgext11gasm mount restricted;
Diskgroup altered.
SQL> alter diskgroup dgext11gasm rebalance;
Diskgroup altered.
If ASM diskgroup is mounted in restricted mode,Database Instance will not be able to access files residing in the ASM Diskgroup
SQL> startup
ORACLE instance started.
Total System Global Area 418484224 bytes
Fixed Size 1300200 bytes
Variable Size 268437784 bytes
Database Buffers 142606336 bytes
Redo Buffers 6139904 bytes
Database mounted.
ORA-01157: cannot identify/lock data file 5 - see DBWR trace file
ORA-01110: data file 5: '+DGEXT11GASM/o11g/datafile/test.256.627345731'
Unlike normal Database Instance, alter system disable restricted session is disabled for ASM Instance.
You need to shutdown and startup ASM Instance in Normal mode to access files reside in the ASM Diskgroup for Database Instance
ASM Instance
=============
SQL> alter system disable restricted session;
alter system disable restricted session
*
ERROR at line 1:
ORA-15000: command disallowed by current instance type
SQL>shutdown immediate
SQL>startup
References
NOTE:429098.1 -
11gR1 ASM New Feature