oracle 11gR2 版本用asmca命令建立磁碟組時,可以選擇 au_size 的大小,比如1M, 4M ,8M,16M

這樣對支援大容量的資料庫非常有好處 ,有以下5個好處：

■ Increased I/O through the I/O subsystem if the I/O size is increased to the AU

size.

■ Reduced SGA size to manage the extent maps in the database instance.

■ Faster datafile initialization if the I/O size is increased to the AU size.

■ Increased file size limits.

■ Reduced database open time.

The allocation unit size is specified with the disk group attribute AU_SIZE. The AU

size cannot be altered after a disk group is created. Example 4–1 on page 4-5 shows

how the AU_SIZE is specified with the CREATE DISKGROUP SQL statement.

For applications that can benefit from large I/O sizes, you can increase the

DB_FILE_MULTIBLOCK_READ_COUNT initialization parameter to 4 MB from the

default of 1 MB. Ensure that the application is thoroughly tested with this new setting

as this change could adversely affect stable optimized plans and future optimizer plan

generation.

To change the DB_FILE_MULTIBLOCK_READ_COUNT setting, use the ALTER SYSTEM

SQL statement, as shown in Example 4–3. This example assumes an 8 K block size.

Example 4–3 Altering the DB_FILE_MULTIBLOCK_READ_COUNT Setting

SQL> ALTER SYSTEM SET db_file_multiblock_read_count=512 scope=both sid=*

See Also: Oracle Database Reference for more information about the

DB_FILE_MULTIBLOCK_READ_COUNT initialization parameter

用asmca建立diskgroup時可以選擇au_size大小，diskgroup一旦建立好後au_size不能修改。

而 oracle 10g au_size 預設大小為 1M，一般情況下是不能修改的，而如果在10g版本中要支援TB或PB的大資料量，那如何修改，下篇文章會有介紹

oracle 11gR2 asm au_size 大小可以自定義

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