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Old 04-29-2008, 12:01 PM   #1
Registered: Feb 2005
Distribution: Ubuntu 8.04
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What's the score with Fake RAID5?

Hey. This relates to a post I made in the Newbie forum (, but I've refined the problem a little more now.

I have a SATA RAID5 array set up via my motherboard (Gigabyte nForce 570). After some reading it seems that the linux kernel is either bugged or simply doesn't support 'Fake RAID5'... At least that's from what I've read on the web for older versions. I'm running Ubuntu 8.04 right now.

The individual drives and the RAID controller are detected in the gnome Device Manager, but cannot be mounted.

Soo, does anyone know what the deal is with Fake RAID5 and linux, specifically Ubuntu? and if there is a simple workaround? I've read that a recompilation of the kernel may be required, if so, has anyone got any good links to tutorials on recompiling to enable Fake RAID5?

Old 04-29-2008, 02:26 PM   #2
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if it's a fake RAID (host CPU based) controller on the motherboard, you are better of just using the software RAID in Linux. Fake RAID won't do anything for you in terms of performance and will probably perform worse than a Linux software RAID (md) setup.

If it's a true hardware based RAID you want, then look at the 3Ware RAID controllers, they have excellent Linux support imho.

You may also want to view the Fake RAID (FRAID) sucks even more at RAID-5 article... and yes it sucks in both Linux and Windows, a shortcoming of the technology and resource usage of the scheme not the OS..
Old 04-29-2008, 03:01 PM   #3
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Cheers for the reply.

Unfortunately I have a lot of data on my RAID drive, which is also used for dual booting to Vista, so reformatting it isn't an option... especailly as it's a TB of data on there!

Soo, whats the score on getting it to work as is... anyone? please?
Old 04-29-2008, 03:27 PM   #4
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Basically you cannot. Fakeraid uses OS drivers to do most of the raid work (by the cpu). These drivers are tied tightly to the OS. As the hardware vendors are not suppling drivers or the specifications to make drivers we are pretty much SOL. Even if they would provide the specifications it would be virtually impossible to make a driver that would allow the use of the array from both OSs(for use on one OS would be hard enough).

For true hardware raid the OS will see just the array and not the actual drives (for the most part). The hardware on the card handles all the delicate operations (whereas the cpu does this on fakeraid). So the drivers for hardware raid are relatively simple.
Old 04-29-2008, 03:51 PM   #5
Registered: Feb 2005
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Hmm. OK, I might have my wires crossed here. To set up my RAID I do it via the BIOS. Does this mean it's not FakeRAID that I have and instead something else? I mean, I boot up off the RAID array, so the OS has no knowledge of the array at that point?

Confused. I don't even know what type of RAID array I have now!
Old 04-29-2008, 06:35 PM   #6
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got dmraid?

It doesn't mean it isn't Fake RAID. All it means is that the OS (Vista I presume) has knowledge of it using a device driver for the CPU to do the RAID work.

Haven't tried it with RAID-5 and Vista myself, but grub and dmraid can access fake-raid from the bios and can be patched for Windows LDM in XP. There's a wiki for fake-raid under Ubuntu. You'll need an initrd (or initramfs) to activate the raid using dmraid.

But you're right, it's not supported "out of the box" for any recent distro I've tried.

Can't disagree with anything anyone else has said about whether it's a good idea - there are definitely better RAID or backup or data integrity solutions.

One problem is that there is a lot of old information out there; I would be careful that you're dealing with information that relates to recent 2.6 kernels and initramfs (not initrd, though slackware's initrd IS an initramfs) I've included a bunch of links I looked through in getting this to work. However, *this* forum usually has the best information.‏‏ --

Hope it helps, happy reading, backup first if at all possible!
Old 05-06-2008, 09:15 AM   #7
Registered: Feb 2005
Distribution: Ubuntu 8.04
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Thanks for all the help. Just a quick update on this...

Turns out that Fake RAID 4/5/6 via dmraid is bugged in the latest kernel - a regression to an earlier bug - but there is a simple fix that has just been posted:

Sorted my problem out no worries.



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