ASM, rebalancing, 3rd party storage and performance

Question

Hi all, I have some questions for the storage experts and I need your opinion about:
1. Which type of ASM is better for the rebalancing perspective (and obviously the performance perspective), but considering the availability as well: Unprotected, 2-way (normal) or 3-way (high)? I know 3-way is the worst because we have to multiply by 3 the space of the database, but has great availability. Which of these do you use in your company?
2. If someone is using EMC/Fujitsu/Hitachi, do you use Unprotected or 2-way (normal) in ASM?
3. Which type of rebalancing (from zero to 11) is the best to use, considering the overall performance , I mean, when you have to add a new disk, ASm will perform the rebalancing.
4. Which is better to use: ASM Cluster File System or Oracle Cluster File System ?
Thanks.

Answer 1

977623 wrote:
1. Which type of ASM is better for the rebalancing perspective (and obviously the performance perspective), but considering the availability as well: Unprotected, 2-way (normal) or 3-way (high)? I know 3-way is the worst because we have to multiply by 3 the space of the database, but has great availability. Which of these do you use in your company?Wrong question IMO. You do not choose normal or high redundancy based on which rebalances the fastest. You make that choice wrt to redundancy and high availability.
The best in this respect is high redundancy. 3 storage servers. Fully redundant I/O fabric layer (3+ I/O paths from each server to each and every LUN). Which means you can loose 2 storage arrays and most of your I/O fabric layer (switches and cables). And the storage layer left will still be able to be effectively used for ASM and the RAC database will not even notice that this destruction happened.
However, this best is not always feasible ito existing architecture, budget and so on. So that drives the requirements and needs and what the best is to meet that.
2. If someone is using EMC/Fujitsu/Hitachi, do you use Unprotected or 2-way (normal) in ASM?That again depends on redundancy levels. If the SAN provides a RAID5 or RAID10 LUN, should you mirror it?
This may makes sense if you have 2 SANS. And with each SAN implementing RAID5, you mirror (via ASM) across SANs.
It makes less sense if you use ASM to mirror (on the same SAN) 2 RAID5 LUNs.
You also may have no choice. For example, migrating a high redundancy diskgroup from a storage server (no redundancy by server), to a SAN (RAID5/10 redundancy by SAN). When migrating ASM diskgroups, you cannot reduce redundancy. You cannot make a high redundancy diskgroup a normal redundancy diskgroup. Or a normal one, an externally redundant diskgroup.
In such a case you normal/high redundancy diskgroup on the new SAN (with its RAID5/10 LUNs), still need its own mirrors in ASM.
3. Which type of rebalancing (from zero to 11) is the best to use, considering the overall performance , I mean, when you have to add a new disk, ASm will perform the rebalancing.How busy is the I/O layer? What production processing is running? How will this be impacted by using power 11? How soon does the old (dropped) disks need to be physically decommissioned? Etc.
There is no single correct answer to what load balancing power setting to use.
4. Which is better to use: ASM Cluster File System or Oracle Cluster File System ?For what purpose?
For RAC database purposes only? ACFS. As OCFS adds another set of kernel drivers, kernel services, and another Interconnect (ocfs needs its own IP Interconnect that is typically run over the public IP network of the cluster, and that can be/should be run over the private IP network of the cluster).
Why add more moving parts (ocfs) when ACFS is available?
Then again - why use ACFS when you are not running Grid Infrastructure? Or why makes your cluster file system dependent on Grid/CRS to be running (with ASM), when OCFS's moving parts are significantly fewer and less complex?
As with most things in Information Technology - there is no overall "best". The "best" depends on a number of factors, and the business requirements that need to be met.