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So Windows 8 is out and I have a new motherboard. I wish to create a RAID 1 coupling between two HDDs -- for storage purposes only (my OS is on an SSD) -- but I don't know which is the best route to take.

My motherboard (Z77 chipset) comes with Intel Firmware RAID, but since I only wish to use my RAID for storage, I wondered if I might be better to use Windows 8 Disk Mirroring?

Can anyone advise which is better? Or perhaps the pros and cons of each, if that's too contentious? I just can't see the benefit of Firmware RAID over Windows Disk Mirroring.

You can see my current setup here, if that might change things(?):

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Thanks!

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Part of it depends whether you need support from other OSes... –  Bob Nov 2 '12 at 5:46
    
Good point, no I don't. –  Django Reinhardt Nov 2 '12 at 5:59
    
Note: Windows storage spaces are not mirroring –  HaydnWVN Nov 2 '12 at 14:25
    
@HaydnWVN I'd actually never even heard of Storage Spaces until that! –  Django Reinhardt Nov 2 '12 at 14:33
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The specific product name is Rapid Storage Technology, sometimes also known as "Matrix Storage Technology." It's a feature usually found in Q, Z and H series chipsets from the past six or seven years. –  Charles Nov 8 '12 at 3:28

3 Answers 3

tl;dr: Last paragraph.

There's some confusion here about the various things that can create a RAID or RAID-like device. Let's discuss the options in order of preference and performance.

Best first: Real RAID cards, from vendors like LSI, Areca and others. These cards usually have dedicated memory for caching and almost always have an optional battery backup unit. The BBU provides power to the cache, so that in the event of an unexpected loss of power, any data that hadn't yet been written to disk won't be lost. Some cards won't let you turn on the write cache unless a BBU is installed. Some of these cards have even more advanced ways of increasing performance. For example, many new LSI cards have an optional add-on called "CacheCade," which can use an SSD for read caching. Real RAID cards also allow you to assign spares, and can automatically begin rebuilding the array in the event of a drive failure.

Next up is OS-provided software RAID. Linux and certain editions of Windows can create devices using various RAID levels. Software RAID is an adequate solution in many cases, but it has a few drawbacks. First, some editions of Windows can't boot off of Dynamic Disks, the feature that creates software RAID. Some (mostly older) Linux distributions also have problems booting off of software RAIDs. Second, software RAID lacks that delicious hardware-backed write cache. It won't save you from data corruption caused by a sudden power loss. Third, depending on the workload and RAID type, it can consume a non-trivial amount of CPU time. This is especially true when using a RAID type that does parity, like 6. I'm not sure about Windows, but Linux's software RAID also allows you to allocate spare drives.

Next is firmware/chipset-based RAIDs, like LSI's 1068 and Intel's "67", "68" and "77"-based RST. Like hardware RAID cards, they expose normal drives to the OS, and don't need drivers to perform basic operation. All of the I/O operations, including parity, are done from within the firmware itself, meaning that they don't use CPU time. Unfortunately they also don't come with any of the benefits of a dedicated hardware RAID, like a write cache or a BBU. It's unfortunate that older Intel RST has a reputation for being flaky and finicky. Firmware RAID usually does not let you allocate spare drives. Unless you do something silly and use RAID 0, you probably won't see any performance improvement using a firmware RAID.

Finally, and worst of all, is fakeraid. There are two classes of fakeraid. The first doesn't require drivers, but usually only exposes RAID 0 and 1. The second requires drivers for all operations, and does everything in software. Fakeraid can be found in inexpensive addon cards, in some cheap consumer-grade NAS devices, and even on some motherboards (usually with an AMD or Nvidia chipset). Like firmware RAID, you almost certainly won't see a performance improvement with fakeraid.

Your question deals with the middle two options: Windows software RAID versus Intel's firmware RAID on a Z77 board. Normally I'd say it's a performance and reliability wash, as both options have proven themselves in the real world and don't overtly suck. As it doesn't look like you're using the mirror as a boot device, I'd usually say that Windows software RAID is probably the most sane way to go. However, the 77-series Intel firmware RAID has a trick up it's sleeve: it can use an SSD as a cache, when you install the optional driver. That is, caching is only available when the driver is loaded. The array itself is always available. If you feel like sticking another SSD in your system, it might work out well.

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So you are saying the initial question is misleading - the RAID controller in questions is not FakeRAID as described, but firmware RAID... –  askvictor Nov 8 '12 at 23:03
    
Bingo. When it was first introduced, it was basically bad enough that it was effectively a fakeraid. It's been nearly a decade since, and the modern implementation has been vastly improved. It's still not great, but it's not going to eat your data for lunch and drink all of the CPU time. –  Charles Nov 9 '12 at 4:58
    
Well, to be fair, both responses you attacked were working on the information given in the question, which was that it was FakeRAID, not firmware RAID. Would have been fairer to sort this out in the question rather than the answers. Anyways, a thorough response. –  askvictor Nov 9 '12 at 5:18
    
+1 Very interesting indeed! It would have been better if you'd commented on my question so I could improve it. Have you got any links to back up your claims about Intel's Firmware RAID not using any CPU? Thanks! –  Django Reinhardt Nov 9 '12 at 15:16
    
@JohnnyW, unfortunately I only have personal experience with it, and the fact that it's never required any drivers to function properly, regardless of OS. Without anything to schedule CPU time with the OS, it's extremely unlikely that it could actually get any. Keep in mind that you're just planning RAID 1, which has minimal processing requirements anyway. –  Charles Nov 9 '12 at 17:51

Since FakeRAID is just still using your CPU, you won't have any performance benefits. Any sort of hardware RAID locks you in - if you need support for the device, you'd better hope they are still supporting it - this is not an issue with software RAID. In short, you're right - there is no real benefit to FakeRAID over software RAID in this scenario (unless you want to add more detail about your use case/product requirements)

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-1, blatantly false. Intel's firmware RAID does not consume any CPU time. The processing is performed entirely by the chipset. –  Charles Nov 8 '12 at 3:30
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@Charles: blatantly false. It is called FakeRAID for a reason: it's not a real RAID controller. en.wikipedia.org/wiki/RAID#Firmware.2Fdriver-based_RAID –  askvictor Nov 8 '12 at 3:32
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Perhaps doesn't require (it does after all run as raid before the is loads) drivers, but almost always used with drivers, which borrow cpu cycles from the host. –  askvictor Nov 8 '12 at 10:43
    
@Charles Intel's "fakeRAID" is software based, and so therefore uses CPU cycles. –  Django Reinhardt Nov 8 '12 at 15:34

Both Windows Mirroring and the Intel FakeRAID will have about the same performance. You will not see real benefits with one over the other due to the fact that they will use your system's resources (CPU) to manage the RAID controller.

This is different from a hardware RAID controller where your controller will do any calculations, lifting the resource usage from your CPU.

However, you will also need to consider that the FakeRAID Controller and Windows Mirroring are both simple functions and that you probably would not see a speed difference between either of those and also the Hardware RAID Controller. The only difference that you would see is that you would have lower cpu usage. This amount is such a low difference that it's negligible.

You may see some real differences if you're using a RAID5/6 where a parity is calculated and written. This takes many more calculations and then would probably want to run some benchmarks to see if FakeRAID is better or worse than Windows Mirroring. Most Hardware RAID Controllers will always win when using RAID5/6.

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You can NOT enable writeback with any fakeraid since that requires battery backed ram on a real raid controller to cache the data in the event of a power loss. Enabling writeback without battery backed ram would violate the interface contract with the OS ( hardware promises data has been written to disk but hasn't ) and lead to a corrupted filesystem if you lost power. –  psusi Nov 8 '12 at 3:20

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