ASM Failgroup best configuration?

Question

Hi experts,
I have a quick question,
If you create a normal redundancy diskgroup through asmca in 11gR2, and choose 4 disks, it will create the diskgroup with failgroup to its own disk.
But in documentation example, we create a diskgroup with specify the failgroup to one or more disks.
my question is what is the best option for specifying failgroup? should it be 1 failgroup for each disk (I don't see why the failgroup is its own disk?) ? or should 1 failgroup consists multiple disk?
Hope you understand my rubbish question
Tx

Answer 1

Hi,
my question is what is the best option for specifying failgroup? should it be 1 failgroup for each disk (I don't see why the failgroup is its own disk?) ? or should 1 failgroup consists multiple disk?Choosing the number of failure groups to create depends on the types of failures that must be tolerated without data loss. For small numbers of disks, such as fewer than 20, it is usually best to use the default failure group creation that puts every disk in its own failure group.
Using the default failure group creation for small numbers of disks is also applicable for large numbers of disks where your main concern is disk failure. For example, a disk group might be configured from several small modular disk arrays. If the system must continue operating when an entire modular array fails, then a failure group should consist of all of the disks in one module. If one module fails, then all of the data on that module is relocated to other modules to restore redundancy. Disks should be placed in the same failure group if they depend on a common piece of hardware whose failure must be tolerated with no loss of availability.
I don't see why the failgroup is its own disk? - -AddFor me it's the opposite. You will take advantages putting disk on same failure group only when you use two or more Storages System, or have common point of failure (like disks sharing the same SCSI controller). If you have no reason to use same failure group, I recommend you puts every disk in its own failure group.
PS: A simultaneous failure can occur if there is a failure of a piece of hardware used by multiple failure groups. This type of failure usually forces a dismount of the disk group if all disks are unavailable.
Regards,
Levi Pereira
Edited by: Levi Pereira on May 16, 2011 9:20 PM