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 andopen 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.
I Think the correct answers are C,E
C:
http://www.oracle.com/technetwork/articles/sql/11g-asm-083478.html
E:
http://books.google.co.uk/books?id=14ZH0eZV6G8C&pg=PA374&lpg=PA374&dq=local+copy+of+an+extent+in+a+stretch+cluster+%28rac%29&source=bl&ots=bshh-P16UB&sig=ooubVe9YwyeZ_JCt0rbaW1i9uQg&hl=en&sa=X&ei=KrpsU_nFKcyXkgWz_oHQBA&ved=0CDMQ6AEwAQ#v=onepage&q=local%20copy%20of%20an%20extent%20in%20a%20stretch%20cluster%20%28rac%29&f=false
Im not sure is A is 100% correct. Documentations says reduce SGA memory requirements for very large databases but doesn´t say anything about metadata or about track extents. Maybe I´m wrong but I would decide for C and E
E is right statement , but doesn’t result from variable extent feature, rather part of ASM Preferred reads feature.
Corrects: A and C.
A because enables faster file opens because of the reduction in the amount of memory that is required to store file extents.
C because ASM automatically size the extents as needed, this is the feature.
A and C
AC
AC
AC
Rebalancing a disk group moves data between disks to ensure that every file is evenly spread across all of the disks in a disk group. When all of the files are evenly dispersed, all of the disks are evenly filled to the same percentage; this ensures load balancing. Rebalancing does not relocate data based on I/O statistics nor is rebalancing started based on I/O statistics. Oracle ASM rebalancing operations are controlled by the size of the disks in a disk group.
Hence, B is ruled out.
The new SYSASM role to manage the ASM instance, variable extent sizes to reduce shared pool usage, and the ability of an instance to read from a specific disk of a diskgroup are just some of the great new features introduced in Oracle Database 11g ASM.
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.
Hence, A is correct.
In Oracle Database 11g, the extent sizes are no longer equal to the AU sizes. The extent size starts at 1MB when the file is created. After the file reaches a certain threshold, the extent size increases to 4MB, then to 16MB, and finally, after a threshold, the extent sizes are 64MB. You don’t have to worry about the sizes; the ASM instance automatically allocates the appropriate extent size. Since a lesser number of extents can accommodate a lot of data, the total number of extents in the shared pool is significantly reduced, improving performance several times
Hence, C is correct.
I would go with A, C.
AC
Yes . A, C are correct