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Re: [rhelv5-list] Best practices on dm-multipath?

On Thu, 29 Nov 2007, D. Canfield wrote:

I've finally got boot-from-SAN hosts running properly off my IBM DS4400 as of the RHEL5.1 beta (I can post my howto if anyone needs it),

Yes. Please do. I am very interested.

and I'm preparing to put a few of these hosts into production. The DS4400 is only capable of failover between paths, not true load balancing, but what I've successfully managed to do is:
- Create two RAID-5 devices on my physical SAN
- Assign each of those devices to a separate HBA
- Use LVM to stripe (RAID 0) those individual SAN devices.

The result is an array with the reliability of RAID 5 and failover HBA's, but with two HBA's and SAN controllers doing the work. Overall, this seems to work well enough, but I'm wondering what any of the experts out there think. Is this safe? Is there a likely bottleneck I'm overlooking that negates the advantages?

I am curious about this as well. I've previously during experimentation done the same thing using software RAID to create a RAID drive from multiple physical SAN devices, but I worry that I am overlooking some reliability problem since no one seems to do this. It *seems* to work, but I want to make sure I'm not overlooking some reliability or subtle corruption problem.

Benjamin Franz

"It is moronic to predict without first establishing an error rate
 for a prediction and keeping track of one’s past record of accuracy."
                    -- Nassim Nicholas Taleb, Fooled By Randomness

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