thanks for your reply, actually the above post was consist of two separate questions. below are these questions.
1)what are the benefits of Rebalance in ASM when we add disks or delete disks(failure) to asm diskgroups?
rebalance increase perfomance by spread data(extents) over all disks in a diskgroup .it is write?
2) >create diskgroup dg2 disk '/dev/sdb1';
so my question here is which redundancy level the diskgoup dg2 will be created ?
Redundancy: You've created a disk group with a single disk. It doesn't make sense for this to be anything other than external redundancy. How can it have failure groups (normal or high) with a single disk?
i am satified with your second answer. diffenately it will create a disk group with external redundancy. i have one more doubt that is if don't specify failgroup while creating diskgroup even though i mention more than one disks then will it create diskgroup with external redundancy ?