2, STEP 3

Exercise 20-2, Step 3:

asm_diskgroups=dg1

If this is not done, you will have to mount the disk group manually every time

you start the ASM instance:

alter diskgroup dg1 mount;

Creating and Using ASM Files

The ASM disk groups are created in the ASM instance; the ASM files are created in the

RDBMS instance. The normal commands for creating datafiles, tempfiles, and log files

can all take a disk group name in place of a filename. For example,

SQL> create tablespace new_tbs datafile '+dg1' size 100m;SQL> alter tablespace system add datafile '+system_dg' size 1000m;SQL> alter database add logfile group 4 '+dg_log1','+dg_log2' size 100m;

The first of these commands creates a new tablespace with one datafile in the disk

group DG1. The second command adds a datafile to the SYSTEM tablespace, in a disk

group created specially for the SYSTEM datafiles; this will probably be a disk group

created with HIGH redundancy. The third command creates a new online log file

group, with two members in different disk groups; these will likely be groups with

EXTERNAL redundancy, because you can rely on the multiplexing to provide fault

tolerance.

To direct archive logs to ASM, set the LOG_ARCHIVE_DEST parameters to point

to disk groups:

P AR T III

SQL> alter system set log_archive_dest_1='location=+dg_arc1';SQL> alter system set log_archive_dest_2='location=+dg_arc2';

It is also possible to direct the flash recovery area to an ASM disk group:

SQL> alter system set db_recovery_file_dest='+dg_flash';

In all these examples, you do not specify a filename, only a disk group. ASM will

generate the actual filenames according to its own conventions. If you wish, you can

see the names by querying views such as V$DATAFILE, V$LOGFILE, or V$ARCHIVED_

LOG, but there is little value in this. A feature of ASM is that it gives you complete

independence from the physical storage: there is no reason for you to want to know

the actual filenames. It is possible to interpret the system-generated names, but they

are not any sort of physical path.