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Re: Data Mirroring on two data centers -- How to use ASM ?

From: Carel-Jan Engel <>
Date: Fri, 19 May 2006 21:06:25 +0200
Message-Id: <>

Hi Madhu,

I'm wondering your primary 'requirement' of mirroring data across TWO data centers.

IMHO, mirroring between data centers is a solution, or if you like, tool. Whatever, it isn't a requirement.

Requirements could be something like:
- After a server failure, the database should be available again within 30 minutes
- After a server failure, no more than 5 minutes worth of transactions may be lost
- After a database corruption, the database should be available again within 6 hours
- After a database corruption, no more than 30 minutes of transactions may be lost
- Restoring of the database to any point in time between now and now - 6 days must be possible   

Then you can start of thinking of how to meet these requirements. This process is well started with thinking of all problems that can pop up. When you have listed the problems it's time to start thinking of countermeasures to come over the problems. It might very well be possible that the solution of having data replicated between two datacenters is not enough, and a local standby might be needed as well. It's impossible to give you a complete list here, it depends totally on the particular environment you're operating in.

When management requires you to use SAN replication, they're taking over your job and responsability. It reminds me to the situation when the right rear wheel of my car was vibrating. I went to the garage and asked them to replace the bearing of the rear wheel (a well known problem of the type of car I was driving then). After paying the bill, nothing had changed. It appeared that rebalancing the wheel would have solved the problem. Lesson learned: If I had told the mechanic the problem, he would have investigated it and applied the right solution. By showing off my 'knowledge' of cars I spent money to solve a non-existent problem, and had to pay again to solve the real problem. Lesson learned: don't push the experts into solutions, but challenge them with problems. Probably you get better solutions, maybe costing less money as well. Of course you are the expert in this case. Management should think in problems, you are the one that provides solutions.

Bottom line: my advice is to go back to the scratchpad, and start defining real requirements, not solutions.

Best regards,

Carel-Jan Engel

If you think education is expensive, try ignorance. (Derek Bok) ===
On Thu, 2006-05-18 at 13:00 -0500, Madhu V wrote:

> Hello All,
> We are planning on testing a two node 10g RAC using ASM for one of our
> database on pSeries using AIX 5.3. We have a primary requirement of
> mirroring data across TWO data centers (Hitachi SAN). I have two
> questions
> 1. Mirroring.
> Can we use AIX Volume Manager to take care of the mirroring or ASM
> to do mirroring. I am specifically looking for HOW and WHY?
> 2. Striping
> I have seen a similar post just a few days ago on ASM striping,
> although i couldn't understand much of it (Pardon my knowledge on disk
> technologies). Our storage folks told me that, they have a huge disk
> cache (128 GB) and very high performing SAN (HDS 9980) w/ excellent
> algorithm for striping the LUNS across multiple disks. So HOW best I
> can use ASM striping along w/ HDS storage striping? or will it cause
> any performance problems??
> Please advise me...
> Good Day,
> Madhu

Received on Fri May 19 2006 - 14:06:25 CDT

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