Why I don't Like Data Guard was Re: Oracle RAC thread

Thanks for the intro ;)

> On Mon, Dec 30, 2013 at 1:15 PM, Dave Morgan <oracle_at_1001111.com <mailto:oracle_at_1001111.com>> wrote:
> On Mon, Dec 23, 2013 at 8:07 PM, Chris King <ckaj111_at_yahoo.ca <mailto:ckaj111_at_yahoo.ca>> wrote:
> We're architecting a new system, and will need 99.5% availability. Looking
>
> I believe this is the wrong metric to use. As others have pointed out it is equivalent to
> ~40hours/year. The correct question is what is the longest outage the business can afford
> for any single event?
>
> 15 minutes, 1 hour, 4 hours?
>
> If the business claims less than 15 minutes they should have real reasons, DataGuard is expensive.
>
> My standard is a simple automatic log ship and apply system from the old days. Train the
> sysadmins to do the failure-over and you can meet a 15 minute deadline during business hours.
>
> Cheap, easy, tested, robust, runs with 3-5 hours of scheduled downtime per year. Every year.
>

First, yes Enterprise edition is expensive, however, if you NEED what Data Guard supplies then it is cheap at the price. However, Data Guard has a much higher maintenance cost also. This maintenance cost is extra administrator time.

Data Guards are dependent on each other. Data Guards require knowledgeable DBAs and sysadmins. In order to be really successful with Data Guard one needs sophisticated developers who can do TAF or auto-magically reread the tnsnames source upon connection failure. So for cases where the business can afford an outage of 15 minutes or so, I can provide a cheaper, more robust solution.

Now that we know where not to use it, lets agree what Data Guard is for and when it should be used.

Most businesses can afford an outage of 15-30 minutes. The only business that can't are those whose transactional databases are intimately involved in the sales process. Telecoms, banking, and airlines for example. Any time the business claims a need of < 15 minute outages make sure you understand why! Loss of revenue or real time access are usually the only real needs, almost everything else fails an ROI test.

If the business has a valid need and DataGuard is chosen to meet it, the first objective , I think, is to be able to perform an automated fail over and the worst any of the "important" clients experience is a 30 second hiccup.

How long is the above going to take? What are you going to use while building and testing the above architecture? What are the total man hours involved?

I can build you a ship and apply system for the time of a single recovery and it will take far less admin time than a Data Guard system. The sysadmins can shut it down, move it, change IP address, whatever they want and as soon as it stands back up it starts working again, as if nothing happened. Shall we go through the steps required to change a Data Guard IP address?

The ship and apply system is simple and easily understood. Nothing more than 2 sql scripts and 3 ten line shell scripts or windows batch files. The 2 databases are completely independent.

Why would I use Data Guard when the business does not need "instantaneous" recovery? Why would I use Data Guard when the infrastructure supports synchronous writes between data centres?

I do not consider more billable hours a valid reason :)

Again I apologize for the aggressive tone of the "Why I Don't Like" subject line.

TIA
Dave

-- 
Dave Morgan
Senior Consultant, 1001111 Alberta Limited
dave.morgan_at_1001111.com
403 399 2442

-- 
Dave Morgan
Senior Consultant, 1001111 Alberta Limited
dave.morgan_at_1001111.com
403 399 2442


--
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