Now that you know you want RAID, it is time to decide whom to appoint to control your array. What do I mean, “Whom to appoint?”
Why, the RAID Controller, of course! There are four broad kinds:
- Software RAID
- Motherboard RAID
- Fake RAID (or Host RAID)
- Hardware RAID
The latest Operating Systems are capable of simple RAID configurations, and are surprisingly fast and efficient. Here’s a list of recommendations of various operating systems with the RAID levels they support*:
- Windows 7 Professional and Ultimate: JBOD, RAID 0 and RAID 1
- Windows Server: JBOD, RAID 0, RAID 1 and RAID 5
- Linux with the mdadm controller: RAID 0, RAID 1, RAID 4, RAID 5, RAID 6, RAID 10 (1+0)
- Mac OS X and Server: RAID 0, RAID 1 and RAID 10
*This is as far as I know. Please check the manufacturer’s website for exact compatibility.
Software RAID works well for non-parity RAIDs like RAID 0, RAID 1 and RAID 10, etc.
Using RAID 5, e.g., when supported, will tax the CPU to make all those heavy parity calculations, and can impact the performance of other software running on the same machine. Modern CPUs have really reduced this ‘problem’, but whether or not this impact is acceptable is for your to decide.
If I had to choose the most robust operating system for RAID, with the best support, I’d choose Linux. And it’s free!
Modern motherboards come with many bells and whistles. For better or for worse, they try to incorporate bits of the CPU, OS, Hard Drive, Memory, etc to increase performance. So why not RAID as well?
Higher-end consumer grade motherboards like the ones made by Gigabyte and Asus sometimes have on-board RAID controllers. Most of the time, the levels are restricted to RAID 0, RAID 1, RAID 5 and/or RAID 10. Be very careful while selecting a motherboard for RAID, not all RAID levels ‘supported’ will work the way you intended to, with the Operating system you use.
The big risk with motherboard RAIDs are that if your motherboard dies, you might have to find the exact same model, or at least a compatible motherboard that also somehow takes all your other hardware. As anyone who has replaced quite a few motherboards will know, this is a scary thought. Why?
Of all the components in a computer, the motherboard tends to be the one with the smallest life cycle. If an OS software RAID crashes, you can re-install the same Operating System and continue working. It’s not that simple if a motherboard dies at the end of its life cycle.
I wouldn’t recommend motherboard RAIDs with today’s technology for consumer-grade computers. However, if you’re running servers, and you only need a simple RAID setup, a motherboard by a good manufacturer like Supermicro might be worth it. Server motherboards tend to have a greater shelf life.
In very loose general terms though, my advice is to stay away.
These are cheap cards that do not contain a dedicated RAID controller chip. Instead they just have a hard drive controller with special firmware and drivers (software).
The burden of RAID processing lies on the CPU, just as in the case of software RAID. This is why it is called ‘Fake’ RAID. Adaptec calls it Host RAID. Usually, these cards only support JBOD, RAID 0 and RAID 1.
The word ‘fake’ isn’t really a fair description. A motherboard RAID is also a kind of ‘fake’ RAID.
You might be thinking, if this card is just software, and the CPU is doing all the work, then what the hell use is it?
It has one exceptional use: You can change your motherboard and your OS, and still keep your drives in RAID. These cards have an even longer shelf life than software or motherboards. It’s another step up.
I recommend this solution over motherboard RAID any day, and in a professional setup, even over software RAID. The company that I recommend for this is Adaptec, and their solution is called Host RAID. The software inside these little beauties is the most important part, so don’t just think of them as adapters.
When looking for a fake RAID solution, check for compatibility with your motherboard, OS and drives.
A hardware RAID is a true RAID Controller that does all the heavy lifting, or at least should. They are mini-computers capable of making their own decisions. Therefore, you shouldn’t be surprised that sometimes they cost as much as a computer.
Hardware Controllers are almost always used in mission critical systems. You will see a familiar trend here – to use specialized components for each separate task. This allows you to change other components or software while continuing to work – the whole point of RAID.
The cost of hardware controllers are governed by how many hard drives it can handle, the protocol (SAS over SATA, etc) and what kind of RAID capability it has. The ‘best’ cards can take many drives and might support many practical RAID levels. Good controllers also come with good software that make installation, maintenance and configurations easy.
Not everything in the hardware RAID world is hunky dory. These are proprietary pieces of gear, and if you suddenly decide one manufacturer isn’t your cup of tea, you can’t move to another without a complete restart from scratch.
On the positive side, these controllers are built to take into account many challenging scenarios in which lesser RAID mortals fail miserably. They usually have caches that store pending writes in case of a power failure. They also guarantee advertised speeds in real world performance, and offer years of trouble-free use.
How it works out for you, though, is dependent on how you plan to use it. Your mileage may vary.
Once you’ve selected the right type of controller, you are ready to put together your RAID system.
Platter Hard Drives
The I in RAID started out as ‘Inexpensive’. Manufacturers quickly got around to changing that to ‘independent’, but we all wish otherwise. The cheapest drives for RAID, especially for large volumes of data, is the simple 7,200 rpm (or 5,400 rpm) Hard disk drive, commonly also called a platter or spinning drive.
You might hear many people harping the merits, resilience or performance of one brand over another. After having used all of these manufacturers over the last 17 years, I can tell you that by the time you buy and setup your RAID array, another manufacturer will have forged ahead in the rat race.
These three manufacturers have been consistently reliable, and at the time of this writing, even though my personal favorite is Western Digital, the most recommended drive for RAID considering longevity is from Hitachi, and the fastest, Seagate. Go figure.
We all know the drill. SSD drives are the future. They are faster and are supposed to last longer than platter drives because they don’t have moving parts. They are also cooler and need less power. Price aside, they are perfect.
SSDs come in two flavors: PCI based, or SATA/SAS based.
For SATA/SAS, I recommend Intel drives.
PCI based drives are much faster and proportionately more expensive. The manufacturer I recommend for PCI based SSD drives is OCZ.
PCI based SSDs make excellent temp/cache/page drives for really fast reads and writes. Also, be careful when trying to build a RAID array with SSD drives – these drives have their own quirks.
One or two drive RAID arrays can be placed inside a PC case. However, external enclosures are the most used method of storing large RAID arrays. There are two ways you can go: bare boxes and boxes with backplanes.
Remember, these systems need power supplies, and possibly additional drive ports depending on the number of drives you have in the enclosure.
We are not finished yet! A good RAID array needs one important device that most people ignore, and pay the price.
I mentioned earlier that human error was the biggest cause of data loss. The second biggest is power failure. A UPS (Uninterrupted Power Supply) gives you that extra time that can turn out to be a life saver.
There’s only one brand I will recommend here, and that is APC.
If you don’t want the hassle of building your own RAID array, you can always buy a ready made system.
At the present moment, the two manufacturers I recommend are Drobo and Western Digital. However, it’s tough to make absolute recommendations in this category because there are many variables, and one needs to carefully study all the options before zeroing in on one particular model.
Guess what, though? You already have the tools to make an informed decision. Go forth and conquer!
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