Oracle Database Automatic Storage Management (ASM)

Welcome to the Oracle community forum and interact with 2 million technical staff. There are many discussions about ASM, but what is ASM? ASM is an effective abstraction layer that enables your Oracle database to be used together with an abstract space called diskgroups, rather than directly using datafiles. This brings many benefits, but it also requires learning some new

Welcome to the Oracle community forum and interact with 2 million technicians> there are many discussions about ASM, but what is ASM? ASM is an effective abstraction layer that enables your Oracle database to be used together with an abstract space called diskgroups, rather than directly using datafiles. This brings many benefits, but it also requires learning some new

Welcome to the Oracle community forum and interact with 2 million technical staff> enter

There are many discussions about ASM, but what is ASM? ASM is an effective abstraction layer that enables your Oracle database to be used together with an abstract space called diskgroups, rather than directly using datafiles. This brings many benefits, but it also requires learning new concepts, commands, usage, and management tasks. So before you invest in your production system, let's look at what it solves, what it manages, and what it looks like.

Why create it?

The best way to answer this question is to directly trace the source, Bill Bridge-the initial architect of Automatic Storage Management. In Oracle ASM in the title of Oracle Press, Bill provides a link where he discussed the problems encountered when managing Oracle data file placement using a file system of a vendor-specific operating system:

1. for archiving logs and backups, the operating system vendor does not provide a shared disk file system.

2. The logical volume manager hides the file location, making it difficult to manage disk I/O and provide good statistics.

3. When the number of disks exceeds 100, the existing lvm cannot work well.

4. When the database has more than 1000 data files, the operating system and Oracle cannot process the database well.

5. It is difficult to name a large number of data files.

6. Features and file system restrictions vary with the operating system.

7. Users at the operating system level can access Oracle files through standard usage, which Oracle does not know.

Therefore, he began to solve these problems by establishing an Oracle file system. His goal is to provide these features:

1. tightly integrated with Oracle and used with clusters (parallel servers ).

2. automatically use the new storage and manage it as a disk unit or disk group.

3. Supports thousands of disks.

4. The file will not be named and will be hidden in the operating system.

Who needs it?

Now, you can quickly browse the above problems and solutions to help you determine who needs ASM. At first, it was used to process a very large online database. So if it includes your store, you may already be following it, or start executing ASM. If your database is small and there are not many data files, you may need some reason to consider using it.

1. You will be familiar with some new technologies, and should start from building them in your development environment and test them for several months.

2. If you want to get higher performance from your existing Disk Subsystem and get better statistics for predicting disk I/O.

3. If you are using RAC, you need to consider ASM.

Start

ASM is managed by an instance and is very similar to an Oracle database. However, the initial parameters are very limited, and the startup process is much simpler.

A. Set your ORACLE_SID to + ASM1

B. Edit init. ora.

# As opposed to RDBMS for a normal Oracle instance

INSTANCE_TYPE = ASM

# These names will be used in place of datafile names when you create tablespaces

ASM_DISKGROUPS = SEAN, AARON

Processes = 100

# This parameter is platform specific and is the path to the raw disk device

ASM_DISKSTRING = '/dev/cciss/c0d0p1 ′

# On 11g you shoshould use diagnostic_dest instead of these

Background_dump_dest =/opt/oracle/admin/+ ASM/bdump'

Core_dump_dest =/opt/oracle/admin/+ ASM/cdump'

User_dump_dest =/opt/oracle/admin/+ ASM/udump'

C. Start the ASM instance

$ Sqlplus/as sysdba

SQL> startup

D. Create a disk group

SQL> create diskgroup SEAN disk'/dev/cciss/c0d0p1 ′;

E. Create a checklist Space

You may guess that creating a tablespace may slightly change. The default method is as follows:

SQL> create tablespace sean_space datafile '+ SEAN' size 1 GB;

But think about this very good feature. If the init. ora file in your database is set:

Db_create_file_dest = + SEAN

You can do this:

SQL> create tablespace sean_space;

Then let Oracle do the rest of the work. In both cases, you will find that the file paths listed in v $ datafile are related to the abstract + SEAN disk group, rather than an actual operating system data file.

F. More

Of course, simplifying the creation of file names and tablespaces is only the tip of the iceberg that ASM can do for you. It also provides a redundancy level.

In terms of databases, the external redundancy capability is mainly when you have redundancy in hardware-level (RAID) or other external methods that Oracle can see. In other words, if asm_diskstring devices use their own logic to hide physical disks behind some redundant hardware layers, you will have external redundancy capabilities.

However, if you do not have this redundancy capability, ASM can provide it. You can specify redundancy, failure groups, and a set of other options to prevent loss of one or more disks, controllers, or even the entire SAM from being invalid. ASM also provides I/O evenly distributed in the disk group. Because ASM has a good understanding of what happened, Oracle can automatically provide you with a better balance between I/O and the disk.

Challenges of Using ASM

Of course, ASM is a powerful technology with great potential. However, every technical solution has many challenges. For ASM, it potentially damages the normal balance of power between the Unix System Management Group and the database/Database Administrator group. Previous groups manage disks, hardware, and operating system levels so that database administrators can work with them to obtain new resources. This will challenge this balance to some extent, and this will cause some resistance from this group.

Finally, it should be caused by business needs. We should also note that ASM is still in the stage of enterprise computing, and it is relatively new. Some vendors have put their core business in the logical space Manager/file system space for many years. In general, maturity is very important for software systems and reliability.

Summary

ASM is very powerful. It provides a solution for the developing large database systems currently deployed. It can also provide solutions for small databases or databases that use clusters. Evaluate, test, and then perform more tests just like any new technology.