Which two statements are true about variable extent size support for large ASM files?
A.
The metadata used to track extents in SGA is reduced.
B.
Rebalance operations are completed faster than with a fixed extent size
C.
An ASM Instance automatically allocates an appropriate extent size.
D.
Resync operations are completed faster when a disk comes online after being taken offline.
E.
Performance improves in a stretch cluster configuration by reading from a local copy of an
extent.
Explanation:
A: Variable size extents enable support for larger ASM datafiles, reduce SGA
memory requirements for very large databases (A), and improve performance for file create and
open operations.
C: You don’t have to worry about the sizes; the ASM instance automatically allocates the
appropriate extent size.
Note:
* The contents of ASM files are stored in a disk group as a set, or collection, of data extents that
are stored on individual disks within disk groups. Each extent resides on an individual disk.
Extents consist of one or more allocation units (AU). To accommodate increasingly larger files,
ASM uses variable size extents.
* The size of the extent map that defines a file can be smaller by a factor of 8 and 64 depending
on the file size. The initial extent size is equal to the allocation unit size and it increases by a factor
of 8 and 64 at predefined thresholds. This feature is automatic for newly created and resized
datafiles when the disk group compatibility attributes are set to Oracle Release 11 or higher.
A,C
A&D
It should be A&C
Extents
The contents of Oracle ASM files are stored in a disk group as a set, or collection, of extents that are stored on individual disks within disk groups. Each extent resides on an individual disk. Extents consist of one or more allocation units (AU). To accommodate increasingly larger files, Oracle ASM uses variable size extents.
Variable size extents enable support for larger Oracle ASM data files, reduce SGA memory requirements for very large databases, and improve performance for file create and open operations. The initial extent size equals the disk group allocation unit size and it increases by a factor of 4 or 16 at predefined thresholds. This feature is automatic for newly created and resized data files when specific disk group compatibility attributes are set to 11.1 or higher. For information about compatibility attributes, see “Disk Group Compatibility”.
The extent size of a file varies as follows:
Extent size always equals the disk group AU size for the first 20000 extent sets (0 – 19999).
Extent size equals 4*AU size for the next 20000 extent sets (20000 – 39999).
Extent size equals 16*AU size for the next 20000 and higher extent sets (40000+).
Figure 1-4 shows the Oracle ASM file extent relationship with allocation units. The first eight extents (0 to 7) are distributed on four Oracle ASM disks and are equal to the AU size. After the first 20000 extent sets, the extent size becomes 4*AU for the next 20000 extent sets (20000 – 39999). This is shown as bold rectangles labeled with the extent set numbers 20000 to 20007, and so on. The next increment for an Oracle ASM extent is 16*AU (not shown in Figure 1-4).
A & C – Correct
AC