Free online RAID calculator can help with project costings

A free online RAID calculator can work out numbers of disks, total array capacity and disk overheads, but what are their limitations and can you do the sums another way?

An online RAID calculator offers an easy way of working out capacities, numbers of disks required and the overheads you’ll encounter in setting up a RAID array. But how useful are these free online tools, and are there any alternative ways of doing the sums you need to do before embarking on a RAID storage array implementation?

In this interview, Bureau Chief Antony Adshead speaks with Martin Taylor, converged network manager with the Royal Horticultural Society, about how to use online RAID calculators, their benefits and limitations, and alternative ways of projecting likely costs and the technical characteristics of storage arrays.

You can download the podcast on RAID calculators or read the transcript. What is a RAID calculator and what are they used for?

Taylor: I’ll give you an example. Say you had an application that required extremely fast disk access but with no resilience at all, just for use for caching files, for example. You take RAID level 0, [and] go to your RAID calculator; depending which [calculator] on the Web that you decide to [use], you can change [the] complexity; some RAID calculators will give you an idea of the array layout whereas some will give you basic figures such as number of disks to how much disk space you get.

[The] Zero Assumption Recovery online RAID calculator gives you quite a large array of options. It allows you to specify your disks and will give you total capacity, what the fault tolerance is, how much space you require to maintain that tolerance, etc. Now, once you get this information, it’s a good indicator of the price you’re going to pay in numbers of drives that you require for each array.

RAID calculators are a useful tool but they rely on a basic knowledge of implementing the correct RAID level for exactly what you want to do with your data. Are online RAID calculators a reliable means of doing the sums you need to do?

Taylor: As a general guide, online RAID calculators are excellent, but, obviously, they will give you a ballpark figure [about how many]  disks you need, how much space overhead, etc., because manufacturers’ RAID controllers assign different levels to these things in your RAID array.

So … it’s great for rough costing but it’s never going to beat the actual deployment on the RAID itself, and you will find the figures will differ from your final implementation. This is not usually by a massive margin so you can give or take a few hundred megabytes either way. … They’re a great indicator for costing projection but I wouldn’t rely on them for exact figures.

Obviously, these online RAID calculators rely on different formulas to [do their calculations]. I’m not a maths genius myself so I haven’t sat down and done the manual calculations for RAID, and these formulas are not easily available on the Web either. … You could pull the code from the calculators if you liked, but all you’re going to get is the same result as … from the formulas. So I wouldn’t say that manual calculation methods are very effective. It would be be time-consuming and complex; and, obviously, the bigger the array the more calculations you’re required to do.

Another way to do this is to look at your existing systems. If you’ve already got RAID in place … you can look at the array configuration utilities on your servers and see how your current arrays are configured, which will give you a good idea of exact overheads on each disk.  

The first stop really should be a RAID calculator online. It’s the first place I go when looking to deploy a RAID array to get a ballpark figure for long-term budgets.

To sum up, online RAID calculators are a very worthwhile tool, they’re free to use, you can go and look through many different ones and get the levels that you like. So, the best thing is to go and Google it and find the RAID calculator that meets the specific need you have in mind.

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