Which two statements are true about the data disk group?

You use the following command to create a disk group:
CREATE DISRGROUP DATA NORMAL REDUNDANCY
FAILGROUP fg_f ra_l DISK
‘/dev/sda6’ NAME FRA_DISKl,
‘/dev/sda7’ NAME FRA_DISK2
FAILGROUP fg_fra_2 DISK
‘/dev/sdb1’ NAME FRA_DISK3,
‘/dev/sdb2’ NAME FRA_DISK4
FAILGROUP fg_fra_3 DISK

‘/dev/sdc1’ NAME FRA_DISK5,
‘/dev/sdc2’ NAME FRA_DISK6
ATTRIBUTES
‘AU_SIZE’ = ‘4M’
‘compatible.rdbms’ = ‘11.1.0’;
Which two statements are true about the data disk group?

A.
Each disk in a failure group is a mirror of the corresponding disk in the other failure groups. For
example,
FRA_DISK2 is a mirror of FRA_DISK4 and FRA_DISK6.

B.
By default, the files created in this disk group must have, for each extent, one primary copy and
two mirror copies; one on each of the failure groups.

C.
Because the size clause is not used, the disk group uses the same amount of space on each
disk.

D.
The ‘compatible. rdbms’ attribute specifies the minimum COMPATIBLE setting for any database
using this disk group.

E.
If the FRA_DISK2 disk fails, there are mirrored copies in one of the other failure groups for any
primary extents that are on FRA_DISK2.

F.
The allocation unit, AU_SIZE, sets the size of the disk read and write to ASM diskgroups.

Explanation:
About Mirroring and Failure Groups
Mirroring protects data integrity by storing copies of data on multiple disks. When you create a disk
group, you specify an Oracle ASM disk group type based on one of the following three redundancy
levels:
Normal for 2-way mirroring
High for 3-way mirroring
External to not use Oracle ASM mirroring, such as when you configure hardware RAID for
redundancy
The redundancy level controls how many disk failures are tolerated without dismounting the disk
group or losing data. The disk group type determines the mirroring levels with which Oracle
creates files in a disk group.
For information about disk group types and templates, see “Managing Disk Group Templates”.
Oracle ASM mirroring is more flexible than traditional RAID mirroring. For a disk group specified
as NORMAL redundancy, you can specify the redundancy level for each file. For example, two

files can share the same disk group with one file being mirrored while the other is not.
When Oracle ASM allocates an extent for a mirrored file, Oracle ASM allocates a primary copy
and a mirror copy. Oracle ASM chooses the disk on which to store the mirror copy in a different
failure group than the primary copy. Failure groups are used to place mirrored copies of data so
that each copy is on a disk in a different failure group. The simultaneous failure of all disks in a
failure group does not result in data loss.
You define the failure groups for a disk group when you create an Oracle ASM disk group. After a
disk group is created, you cannot alter the redundancy level of the disk group. If you omit the
failure group specification, then Oracle ASM automatically places each disk into its own failure
group, except for disk groups containing disks on Oracle Exadata cells. Normal redundancy disk
groups require at least two failure groups. High redundancy disk groups require at least three
failure groups. Disk groups with external redundancy do not use failure groups.
Allocation Units
Every Oracle ASM disk is divided into allocation units (AU). An allocation unit is the fundamental
unit of allocation within a disk group. A file extent consists of one or more allocation units. An
Oracle ASM file consists of one or more file extents.
When you create a disk group, you can set the Oracle ASM allocation unit size with the AU_SIZE
disk group attribute. The values can be 1, 2, 4, 8, 16, 32, or 64 MB, depending on the specific disk
group compatibility level. Larger AU sizes typically provide performance advantages for data
warehouse applications that use large sequential reads.
Oracle Automatic Storage Management Administrator’s Guide
11g Release 2 (11.2)