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because ASM stripes all data accros all Disk with the same data size you can get a out of disk space if you put a smaller and a bigger disk in the same diskgroup. If the smaller disk gets full ASM raise a out of disk space even there is space on the bigger disk.
Unbalanced disk can cause disk lacking sufficient free space makes it impossible to do any allocation in a disk group because every file must be evenly allocated across all disks per ASM stripping policy.
Unbalanced disk configuration and certain operations on ASM disks can create this type of problem. The problem frequently should be resolved after a succesfull rebalance as far as all disks have the same storage capacity and there is no underlying hardware problems.
The most common reasons can be as follows:
*1- Capacity of disks within ASM diskgroup are different*
2- ASM instance is shutdowned normal/immediate before a rebalance is completed.
3- Disk is DROPPING / HUNG state
4- After an add disk command the rebalance is still in place
Edited by: Levi Pereira on Oct 10, 2012 4:41 PM : As peter mentioned above!!!
Saikat Banerjee wrote:YES
Is there any effect on performance if I keep various disks with different sizes in the same disk group?
Is it recommended to keep the size of disks in same diskgroup equal?..If yes, why?You might want to get the book " Automatic Storage Management - Under-the-Hood - a Practical Deployment Guide"
If a BIG disk fails and tries to rebalance that data to the smaller disks - will it fit? Probably not. Then you have a major problem.
Bottom line: EXPLICITLY FOLLOW THE RECOMMENDATION. If you don't, you may want to keep your resume up to date.