12.2 Flex Disk Groups

xychong123發表於2017-07-13
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Automatic Storage Management Administrator's Guide

-----Managing Oracle ASM Flex Disk Groups

An Oracle ASM flex disk group is a disk group type that supports Oracle ASM file groups and quota groups.

In general, a flex disk group enables users to manage storage at the granularity of the database, in addition to at the disk group level.

The following are characteristics of a flex disk group:

  • The redundancy of files in a flex disk group is flexible and enables storage management at the database level.

  • File groups of flex disk groups are used to describe database files.

    Each database has its own file group, and storage management can be done at the file group level, in addition to the disk group level. For example, you can specify different redundancy and rebalance settings for different file groups. File groups are associated with a quota group, enabling easy quota management.

  • The redundancy setting of a flex disk group is set to FLEX REDUNDANCY and each file group of the flex disk group has its own redundancy property setting.

  • A flex disk group generally tolerates two failures, the same as a HIGH redundancy disk group.

    However, if the disk group has fewer than five failure groups, then it can only tolerate one failure. This restriction is the result of the quorum requirement of the disk group.

  • The failure tolerated by a database is dependent on the redundancy setting of its associated file group in the flex disk group.

  • A flex disk group requires a minimum of three failure groups.

  • Migrating (converting) to a flex disk group can be performed for a NORMAL or HIGH redundancy disk group with the CONVERT REDUNDANCY TO FLEX clause of the ALTERDISKGROUP SQL statement. You cannot migrate an EXTERNAL redundancy disk group to a FLEX redundancy disk group.

  • When migrating to a flex disk group, the disk group must have a minimum of three failure groups and must be mounted in restricted mode (MOUNTED RESTRICTED) for the duration of the migration.

  • The default size of the allocation unit (AU) is 4 M.

  • The Virtually Allocated Metadata (VAM) is enabled and required for a flex disk group.

  • The COMPATIBLE.ASM and COMPATIBLE.RDBMS disk group attributes must be set to 12.2 or greater.


Example 4-15 Adding a File Group to a Database 

ALTER DISKGROUP DiskGroup_1 ADD FILEGROUP FileGroup_PDB1
    DATABASE PDB1
    SET 'quota_group' = 'QuotaGroup_QGRP1';

ALTER DISKGROUP DiskGroup_1 ADD FILEGROUP FileGroup_PDB2
    DATABASE PDB2
    SET 'quota_group' = 'QuotaGroup_QGRP2';

Example 4-16 Modifying a File Group 

ALTER DISKGROUP DiskGroup_1 MODIFY FILEGROUP FileGroup_PDB1
    SET 'datafile.redundancy' = 'HIGH';

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