Oracle Database 11gR1 和 10gR2 ASM Best Practices 說

在Metalink上找到了一個Oracle Database 11gR1 和 10gR2 ASM Best Practices 的說明文檔，一共是40頁，花點時間，看了一下，主要講的還是一些ASM的基礎知識。 不過了解這些對理解ASM 是很有必要的。

下載Oracle Database 11gR1 和 10gR2 ASM Best Practices

看的時候，覺得一些注意的地方，都copy了一份，粘貼如下：

1. ASM 的限制：

ASM has the following size limits:

（1） 63 disk groups in a storage system

（2）10,000 ASM disks in a storage system

（3） 1 million files for each disk group

2. ASM 的鏡像

       ASM uses a unique mirroring algorithm. ASM does not mirror disks; rather, it mirrors extents. As Thus when a block is written to a file, each extent in the extent set is written in parallel. However, when a block is read from disk, it is always read from the primary extent, unless the primary extent cannot be read.

       ASM 采用的是extent級別的鏡像，而非disks，在寫extent的時候，是并行寫，但是讀的時候，僅從primary extent進行讀，除非primary extent 不可以用的時候才會去讀mirror extent。

       這一點和我們的RAID 鏡像有一定的區別。

3. ASM 內存設置

       The SGA parameters for database instance needs slight modification to support ASM extent maps and other ASM information. Note if the 10g Automatic Memory Management feature is being used on the database instance, then the following sizing data can be treated as informational only or as supplemental data in gauging appropriate values for the SGA. Oracle highly recommends using the Automatic Memory Management feature.

       The following are guidelines for SGA sizing on the database instance:

（1）Processes = Add 16

（2）Shared_pool = Add additional 600k

（3）Large_pool – Additional memory is required to store extent maps. Aggregate the values from the following queries to obtain current database storage size that is either already on ASM or will be stored in ASM. Then determine the redundancy type that is used (or will be used), and calculate the shared_pool, using the aggregated value as input.

select sum(bytes)/(1024*1024*1024) from v$datafile;

select sum(bytes)/(1024*1024*1024) from v$logfile a, v$log b

where a.group#=b.group#;

select sum(bytes)/(1024*1024*1024) from v$tempfile where status='ONLINE';

For diskgroups using external redundancy = (Every 100Gb of space needs 1Mb of extra shared pool) + 2M

For diskgroups using Normal redundancy: (Every 50Gb of space needs 1Mb of extra shared pool) + 4M.

For diskgroups using High redundancy: (Every 33Gb of space needs 1Mb of extra shared pool) + 6M.

這個是一個10g RAC 測試平臺的默認值：

SQL> select instance_name from v$instance;

INSTANCE_NAME

----------------

+ASM1

SQL> show parameter processes

NAME                                 TYPE        VALUE

------------------------------------ ----------- ------------------------------

aq_tm_processes                      integer     0

db_writer_processes                  integer     1

gcs_server_processes                 integer     1

job_queue_processes                  integer     0

log_archive_max_processes            integer     2

processes                            integer     40

SQL> show parameter share

NAME                                 TYPE        VALUE

------------------------------------ ----------- ------------------------------

hi_shared_memory_address             integer     0

max_shared_servers                   integer

shared_memory_address                integer     0

shared_pool_reserved_size            big integer 2516582

shared_pool_size                     big integer 48M

shared_server_sessions               integer

shared_servers                       integer     0

SQL> show parameter large_

NAME                                 TYPE        VALUE

------------------------------------ ----------- ------------------------------

large_pool_size                      big integer 12M

--這里的large pool 需要結合自己的業務進行調整

4. ASM 實例和DB 實例之間的關系

       Since ASM manages diskgroups and hold the database files and its metadata, a shutdown of the ASM instance will cause all client-database instances to shutdown as well.

       In normal shutdowns, the ASM instance will begin shutdown and wait for all sessions to disconnect, just as typical database instances.

       Note, however that ASM has a persistent database instance connection, thus the database instances must be shutdown first, in order for ASM to complete shutdown.

--DB 實例先shutdown 之后 ASM 實例才能shutdown

       In case of ASM SHUTDOWN IMMEDIATE or ABORT, ASM will immediately terminate any open connections (including the database instance connections), and as a result, all dependent databases will immediately abort; i.e., databases will ungracefully shutdown.

       In a single ASM instance configuration, if the ASM instance fails while diskgroups are open for update, ASM instance recovery will be performed upon the restart of ASM by reading the disk group logs.

       In RAC environments, with multiple ASM instances sharing disk groups, if one ASM instance should fail, another node’s ASM instance automatically recovers transient ASM metadata changes caused by the failed instance; i.e. performs instance recovery.

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