Scalability and Reliability

[srivastava ashish]

Question :- if i increase the number of webservers what will increase ?(choose one)
a)Scalability
b)Reliability

which and why?

[Claudiu Dumitrescu]

b)Reliability

As I see it, scalability is the capability of a system to handle a growing amount of loading provided with additional resources, while the reliability will assure the system still respond correctly when under heavy load.

Now, adding more servers to your system is something made possible by the scalability attribute of your system but will not increase the attribute. It will just scale the system.

On the other hand, adding more server could indeed help with reliability of your system if not from else at least because it just unload it.

So, the bottom-line: improved scalability is an enabler for adding more servers and reliability is a consequence of it.

Probably, I got it all wrong.

[srivastava ashish]

since i have added more webservers it should be able to handle more user requests henceforth growing scalability .
Reliability can depend on a lot of factors than just incoming traffic .So the question still stands ground .

However you will be pleased to know that your answer is correct (read it somewhere) but i can't really get the justification.

[Meeti Khare]

Hi Ashish,


I think it will increase both, but since here in the question there is no mention of load increase and
"Reliability is the ability to ensure that the product is trustworthy and dependable for all of its transaction. The system load, for example, should not have any effect on the correctness of the system transaction for a system to be reliable."
So if suppose for some reason 1st webserver is down then other will serve the request with the same response hence the system is reliable.

[srivastava ashish]

Meeti,

Good point ..but question does not mention load balancing algorithm as well..But may be we can safely assume that reliability is of high concern that scalability so Reliability could be the answer.

[Claudiu Dumitrescu]

To better grasp my point let me put this question:

What capability will benefit if you choose a 3-tier architecture over a 1-tier?

a)Scalability
b)Reliability

You see? Adding more servers prove the scalability of your system but can do nothing to improve it. On the other hand decisions like the one in the question can indeed improve the Scalability.

[Andrew Monkhouse]

Duclad

Please check your private messages regarding an important administrative matter.

Also, please note that you must mention the source of questions, or the topic is likely to be deleted (see the forum FAQs for more details).

-Andrew

[Claudiu Dumitrescu]

Well, the question is something I came up to better serve my explanation.