Would like to ask a quick question on ASM diskgroup using normal redundancy (2 way mirroring).
Is it possible to mount and open a ASM diskgroup (using normal redundancy) with one side of the mirror only?
Are there are any procedures for this? I have looked through the documentation but could not find any information on this.
The best I could find is:
Mounting and Dismounting Disk Groups
Has anyone experienced and managed to recover such a situation e.g where the RAC goes down and 1 side of the mirrored ASM group is lost while the other side of the ASM group is still intact?
As you know, we can use mount or dismount for only disk group.
If we sure 1 side of normal redundancy failed or corrupted, then we can drop this disk and add new disk to this group.
(with one command) and not forget rebalance for this diskgroup. (for more information read ASM rebalance)
How to RAC going down? Have any backup of OCR and VOTE ?
ASM is not a software RAID, though the configuration with only two disk groups may suggest a similar striping fashion. A RAID creates identical disks on a disk block level. ASM does not and works on the level of file extents and striping based on allocation units. For instance, imagine if you have setup 2-way redundancy with 3 disk failure groups. How would you split the mirror? You won't loose data when one disk failure group goes offline, that's for sure, but you cannot be sure the offline disk group happens to be a complete copy. As such, using an offline disk group for the purpose of data retrieval does not seem to make much sense.
A good resource is a book called "Automatic Storage Management: Under the Hood"
This will give you a detailed explanation on how ASM functions. This is for 10g/11g.
If you do not have any hardware/sys-admin experience, this is a must-have in your tool box. Because of the complexity of ASM and RAC, I would HIGHLY recommend that you spend time understanding system administration, network administration and SAN administration. The question to ask yourself: "How can I properly configure a high performance, highly available 'system' if I don't understand the inner workings of that system and how all of the parts play together?"