How many disk groups for +DATA?

Question

Hi All,
Does oracle recommends having one big/shared asm disk group for all of the databases?
In our case we going to have 11.2 and 10g rac running against 11.2 ask...
Am I correct in saying that I have to set asm’s compatibility parameter to 10 in order to be able to use the same disk?
Is this is a good idea? Or should i create another disk group for the 10g db’s?
I’m assuming there are feature that will not be available when the compatibility is reduced to 10g...

Answer 1

Oviwan wrote:
what kind of storage system do you have? nas? what is your protocol between server and storage? tcp/ip (=>nfs)? fc?....
if you have a storage with serveral disks then you create mostly more than one lun (raid 0, 1, 5 or whatever). if the requirement is, that you need a 1 TB diskgroup, then I would not create 1 1TB lun, I would create 5x200GB lun's for example, just for the case that you have to extend the diskgroup with a same lun size. if its 1 TB then you have to add another 1TB lun, if there are 5x200GB luns then you can simply add 200GB.
I have nowhere found a document that says: if you have exactly 16 lun's for a diskgroup it's best. it depends on os, storage, etc...
so if you create a 50gb diskgroup I would create just one 50gb lun for example.
hthyes its NAS, connectd using Iscsi. it has 5 disks 1TB each and configued with RAID5. I found below requirments on asm ... it indicates 4luns as minimum per diskgroup, but it doesnt clearify whether its for external redundancy or as mredundancy types.
•A minimum of four LUNs (Oracle ASM disks) of equal size and performance is recommended for each disk group.
•Ensure that all Oracle ASM disks in a disk group have similar storage performance and availability characteristics. In storage configurations with mixed speed drives, such as 10K and 15K RPM, I/O performance is constrained by the slowest speed drive.
•Oracle ASM data distribution policy is capacity-based. Ensure that Oracle ASM disks in a disk group have the same capacity to maintain balance.
•Maximize the number of disks in a disk group for maximum data distribution and higher I/O bandwidth.
•Create LUNs using the outside half of disk drives for higher performance. If possible, use small disks with the highest RPM.
•Create large LUNs to reduce LUN management overhead.
•Minimize I/O contention between ASM disks and other applications by dedicating disks to ASM disk groups for those disks that are not shared with other applications.
•Choose a hardware RAID stripe size that is a power of 2 and less than or equal to the size of the ASM allocation unit.
•Avoid using a Logical Volume Manager (LVM) because an LVM would be redundant. However, there are situations where certain multipathing or third party cluster solutions require an LVM. In these situations, use the LVM to represent a single LUN without striping or mirroring to minimize the performance impact.
•For Linux, when possible, use the Oracle ASMLIB feature to address device naming and permission persistency.
ASMLIB provides an alternative interface for the ASM-enabled kernel to discover and access block devices. ASMLIB provides storage and operating system vendors the opportunity to supply extended storage-related features. These features provide benefits such as improved performance and greater data integrity.
one more question about fdisk partitioning. is it correct that we should only create one partition per luns (5x200Gb luns in my case) is it because this way i will have more consistent set of luns( in term of performance)?