[one daily question] 11gOCP 1z0-053:2013-10-8 attribute for a individual disk group ............ 73____div

Reprint please indicate the source: http://blog.csdn.net/guoyjoe/article/details/12508471

Correct answer: E

Oracle Databae 11g introduced a new concept called the ASM attribute. These properties provide a granular control of the disk group level for DBAs. The properties that you can set are listed below.

1. Allocation unit (AU) size. Starting with Oracle Database 11g, you can give au when you create a disk group. Au size can be 1MB, 2MB, 4MB, 8MB, 16MB, 32MB, 64MB.

2, Compatible.rdbms property.

3, Compatible.asm property.

4, in minutes (M) or hours (H) as the unit of Disk_repair_time.

5, the redundancy properties of the specific template.

6, the stripping properties of the specific template.

These properties of the disk group can be established at Create DiskGroup and can be modified later with the Alter DiskGroup command. You can query all disk group properties from the V$asm_attribute view.

The Disk Group command is created as follows:

Create DISKGROUPDG1

Disk '/dev/raw/raw1 ',

'/dev/raw/raw2 ',

'/DEV/RAW/RAW3 '

Attribute ' compatible.asm ' = ' 10.1 ';

Aler diskgroup dg1set attribute ' compatible.asm ' = ' 11.1.0.0.0 ';

Size of allocation unit

Before Oracle database11g, the allocation unit (allocated Unit,au) dimension could not be specified when creating a disk group. All au are 1MB. There can be multiple au_size in Oracle Database 10g, but not many DBAs know. Specifying Au_size in Oracle Database 10g means setting an underscore initialization parameter and creating a disk group. If you want more than one AU dimension, you must set the initialization parameter and restart the ASM instance with the new AU dimension. The following underscore initialization parameter allows a 16M au ruler and a 1M au dimension. This sizing step is recommended only for VLDB databases, which may also apply to databases with large objects (BLOBs and CLOB):

_asm_ausize=16777216

_asm_stripesize=1048576

In Oracle Database 11g, the Au_szie property is specified only when a disk group is created. Because the storage attribute is involved, this property cannot be modified with the Alter DISKGROUP command.

Starting with Oracle Database 11g, you can set the ASM allocation Unit (AU) size to start at 1MB, with a power increment of 2 straight 64MB. The larger au is good for large VLDB databases or data warehouses that perform a large number of sequential reads. In addition, companies that store blobs or securefile in the database also benefit from the larger AU.

1. Variable size

Variable size (variable-sizeextent) provides support for large ASM files. This feature reduces the SGA requirements for managing RDBM instance Central maps (extent map).

2, manual allocation of large areas

Starting with Oracle 11g, you can assign larger extents when you create a disk group. You can create a disk group with a larger au rather than a 1M size area. You can use the Create DiskGroup command and set the appropriate properties of the disk group to change the DG1 Disk group's allocation unit size to 16MB, as follows:

Create DISKGROUPDG1

Disk '/dev/raw/raw1 ',

'/dev/raw/raw2 '

Attribute ' au_size ' = ' 16M ',

' Compatible.asm ' = ' 11.1 ',

' Compatible.rdbms ' = ' 11.1 ';

II, RDBMS and ASM compatibility

There are two compatibility settings for ASM and the database. When DBAs consider compatibility, they think of initialization parameters in the Init.ora file or spfile that indicate what version of the ASM or database instance can get. The compatible parameter is one of two compatibility settings. You can set the compatible parameter for an ASM or database instance. The legal compatible values for ASM and database instances are given below:

10.1;

10.2;

11.1;

Obviously, 10.1 is the lowest level of compatibility because ASM is introduced as a new feature of 10.1. Setting the initialization parameter to a value less than the software version excludes the new features introduced in the new version. For example, if you set the compatible parameter 10.2 for an ASM instance of 11.1, the Oracle 11g new feature will not be available.

Another compatibility setting applies to the capabilities provided by ASM disk groups and disk groups. There are property settings at the disk group level that control what features are available to the ASM Disk group and what features are available at the database level. These properties are called ASM compatibility (COMPATIBLE.ASM) and RDBMS compatibility (COMPATIBLE.RDBMS). At each disk group level, you can adjust both of these compatibility settings to meet business or technical requirements. Disk group compatibility information is stored in disk-group metadata and provides multi-level support for different versions of the database (10g, 10g Release 2, and 11g).

Three, fast mirror sync

In Oracle Database 10g, ASM takes the disk offline when it cannot write a section or access the disk and the disk is no longer needed, in short, by removing the disk from the disk group. At this point, ASM will use a mirrored copy to make a balance on the area of the disk members that the disk group retains.

In Oracle 11g, Oracle assumes that the contents of the deleted disk are not corrupted or modified and retains its membership in the disk group. Oracle introduces an attribute called ASM fast disk resynchronization (ASM fast resync) that does not automatically remove disks from the disk group for write failures. Now, when a disk is offline, Oracle tracks all extents modified for a specific time and retains the disk's membership in the disk group.

1, Disk modification time

In Oracle 11g, the fast mirror-sync feature is implemented with the grace period (grace period) assigned to repair the offline disk. There is a new Disk group property, named Disk_repair_time, that allows you to specify the maximum time before the failed disk is removed from the disk group. Disk_repair_time is used to prevent the disk from being removed from the disk group because the cost of a heavy-sync operation is much less than the balance operation. The default value for Disk_reprair_time is 3.6 hours or 12,960 seconds.

2. Disk online and offline

Together with this wide-period property of the disk group, Oracle 11g ASM also provides the online option for the Aler diskgroup command to initiate disk resynchronization operations. The following statement marks redundant copy replication as obsolete for all extents:

Alter diskgroupdisk dg_100 Online;

Similar to bringing a disk online, you can take one disk offline using the following SQL command for preventative maintenance alter DISKGROUP disk offline:

Alter diskgroup Data Offline disk dg_200 drop after m;

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