# [Solved] On Board Software RAID && dual boot

## MaximeG

Hi,

I'm about to get a new MSI Eclipse plateform which is RAID capable.

My friend says that while Windows will see the software raid and use my capacity as a single nice fat drive, Linux will basically not see it.

He claims that Linux will see my 2 drives as they are (sda & sdb) and therefore it will not work nicely (data corruption) due to the difference of settings between linux and windows.

Is it somehow true ? Do we have a mean to workaround this ? Is Linux really insensitive to onboard software raid ?

I've never done RAID before, so hence my message  :Smile: 

Thanks !

Maxime

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## richard.scott

The thing your looking for is called dmraid... 

This thread may help:

https://forums.gentoo.org/viewtopic-t-750872-highlight-dodmraid.html

or this on the Wiki:

http://en.gentoo-wiki.com/wiki/RAID/NVRAID_with_dmraid

You need to add "dodmraid" to your LiveCD when booting it and it should detect your Motherboard raid setup.

You may need the latest LiveCD tho?

Rich

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## MaximeG

Thanks !

And I guess I can reproduce that dodmraid 'option' in grub (config kernel file line), so it will be recognized at boot after installation ?

Regards,

Maxime

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## richard.scott

 *MaximeG wrote:*   

> Thanks !
> 
> And I guess I can reproduce that dodmraid 'option' in grub (config kernel file line), so it will be recognized at boot after installation ?
> 
> Regards,
> ...

 

yep, that's the idea.

you'll need to create a "genkernel" style kernel tho.... and believe me that's the easier way.

Rich.

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## MaximeG

All right,

Thanks for your precious advises.

Looks like I have some other things to discover and have to spend some time to investigate ^^.

Maxime

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## pigeon768

It *should* work fine. Linux has supported hardware bound software raid (I don't even know what to call it. It's not software raid and it's not hardware raid either) for years and years now. I used such a system starting in 2002, although now I'm using kernel based software raid.

The MSI Eclipse uses a JMicron controller. Does anyone know if this controller works in AHCI mode? If it doesn't - buy a different motherboard and save yourself the trouble. JMicron isn't just cheap (in a bad way) hardware, they don't really foster linux driver development.

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## MaximeG

I see,

Well, I will look if I can find another MB that provides the same features as the MSI but with another controller, but since the raid device isn't really at the top of my requests list, I'm not very keen to change my choice.

Do you happen to know what kind/brand of onboard controller I should look for ?

Thanks && Regards,

Maxime

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## richard.scott

If you don't need Linux to access your Windows data then I'd not worry about trying to setup the motherboard raid. I'd go for Software Raid instead as this will work just fine. Your windows partitions will use the motherboard raid and drivers and linux can use its own raid software.

Also, if your only using this platform to learn more linux stuff then why not install Linux inside VMWare on your Windows system?

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## MaximeG

@Richard.Scott

Linux is my main Operating System for a couple years now, so I would certainly not virtualize it in favor of Windows !

I unfortunately still need Windows though for some games (although I try at maximum to have them running on Linux).

I don't think I'd need to access my windows data with my Linux though, but my friend told me that using the MB Raid with windows and the Kernel Raid with Linux may lead to data corruption. I don't know what's the truth here since I'm almost ignorant in anything regarding Raid.

But would it be OK to do such a thing with dual boot, how Grub will behave ? 

@ Pigeon768

I looked for an MSI alternative with the Asus P6T, it's using the same JMicron controllers. I believe that I'll go for the MSI and stop worrying. If the raid doesn't work, I'll consider buying a hardware controller on an additional card later, when I'll be ready to move to raid. I saw some interesting, Linux supported, cards at less than $100.

The good news are, some people that bought those MB told everything is Linux "supported and works", for what it's worth  :Wink: 

Thanks and Regards,

Maxime

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## richard.scott

The only reason Linux may corrupt data is if you tell it to use the same partitions on each disk that windows uses.... if you do that your bound to loose data   :Wink: 

If you keep thinkgs on different partitons then once you've installed Windows you can then install Linux.

You would need to remember to install the Grub MBR on both disks... this is a good resource for help:

http://en.gentoo-wiki.com/wiki/RAID/Software

Rich

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## MaximeG

Super,

Will try !

Maxime

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## MaximeG

Hi,

What would be the best then ? On-board or Kernel Raid ? I guess the major decision point would be performance here.

Because as it was said in this thread, if I want to access my Windows data I need to do the dmraid (on-board) thingy. Since it's likely to happen (not on a regular basis though) I'd rather follow this path.

Now if the kernel raid is twice better, I may reconsider it though.

I know it's somewhat silly a question, but I'm a total noob at raid :/

Thanks !

Maxime

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## richard.scott

As both don't interact you can setup both onboard kernel for windows partitions and software raid for linux.

However, for ease of use, why not just try setting up dmraid (onboard raid) and see how it goes?

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## MaximeG

I think that's what I'm going to try.

However, a friend of mine told me that the on-board software raid will be (way?) slower than the kernel one. This because the first will be driven by the ICHR SouthBridge (Intel Matrix Data Storage) while the latter will be managed by the Intel CPU, which is obviously x times faster.

Now, the question would be, what's the performance difference ? If it's 5% I don't really care. If it's 100% I may consider using the kernel :p

Thanks for your answers so far  :Smile: 

Maxime

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## richard.scott

This may help:

dmraid FakeRAID vs Linux Software RAID

Not sure how accurate it is tho?

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## MaximeG

Thanks !

15% better for hdparm, 24% for bonnie. Looks like the kernel raid worth it. (although indeed, the quick benchmark results are somewhat skewed)

Isn't it too heavy computing for the CPU though ?

[EDIT] In the Raid software wiki, I can see this :

 *Wiki wrote:*   

> Software RAID is compatible with a dual boot environment involving windows but windows will not be able to mount or read any partition involved in the pure software RAID, and all pseudo-hardware RAID controllers must be turned off. 

 

Does it mean that I can't have Windows using the on-board raid if I use the kernel raid with Gentoo ?

Regards,

Maxime

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## richard.scott

You can't use both RAID types on the same device, but AFAIK they can co exist on different partitions on the same disk e.g:

partition1 = Windows

partition2 = linux

partition3 = swap

partition4 = linux

Having the raid switched on in the bios makes no difference to Linux unless you tell it to use it.

You also need to use device names different to the standard /dev/sda and /dev/sdb etc.

Rich.

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## MaximeG

Hi,

I installed Windows on the Intel firware raid0 array.

I booted up with Gentoo to see what I can see, and there are

/dev/sda

/dev/sda1

/dev/sdb

And that's it. It looks like gentoo doesn't see anything on the second drive. I looks like compromised for the following set :

Windows on firmware raid0 (sda + sdb)

Linux Kernel software raid0 (sda + sdb)

Therefore, I think I'll go for :

Windows on firmware raid0 (sda + sdb)

Linux dmraid mapper raid0 (sda + sdb)

Thanks for you answer anyways !

Maxime

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## lyallp

I tried, a while ago, to mirror 2 750G disks, whereby I have about 250G set aside as /boot, / and LVM for my linux and 500G as a Windows NTFS Partition, for my dual boot machine. (I boot windoze to play games, occasionally).

I ended up partially giving up as I could not get linux and Windows to agree on the windows partitions mirroring.

I have now got my 250G linux paritions mirrored, using mdadm,  and I use the other two 500G partitions as separate NTFS-3g partitions, which both linux and windows can see.

I figured that nobody keeps anything in valuable in ntfs so it didn't matter if they where not raided.  :Smile: 

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## MaximeG

D'oh.

Looks like it's harder than I thought :p

But here, I'm doing raid 0 for performance, not to protect my data. So I unfortunately can't do the same as you.

Regards,

Maxime

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## MaximeG

Hi,

Got it working with dmraid.

I'm able to see Windows partition (dual boot with Vista), and performances are good : around 195% of the original speed for a stripping raid (raid0), while the theoric limit is 200%  :Smile: 

I suspect the performances would be less impressive for a more complicated raid (like raid5) that requires more computing though.

Thanks to richard.scott and his usefull link !

Regards,

Maxime

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