# fakeraid for windows, kernel softraid (md) for linux?

## dirk_salewski

Hello NG, 

recent mobos mostly have some sort of bios raid, which can be used with dmraid if you want to dual-boot windows. However, 

as shown on http://blog.shaf.net/?p=6 kernel softraid (md) beats fakeraid (dmraid) on performance

if your mobo dies you need another mobo with same chip (say ICHxR) to get access to your data, whereas md would (in theory) allow to move on to a different mobo without problems

afaik at least ICHxR in RAID mode shows up as normal ahci controller unless using dmraid, without losing functions like ncq and the like

Wouldn't it be possible then to use the bios raid functions for installing a gaming windows raid0 (when it dies, it dies, so what), and access the free rest of the disks just normally, to build a "real" kernel softraid on it? 

Can anybody confirm point three, and did anyone try this? If it works I'd probably buy a ICH9R-based board, if not I'd probably go with a (cheaper) non-raid ICH9-model. 

Greetings, 

DS

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## likewhoa

 *dirk_salewski wrote:*   

> as shown on http://blog.shaf.net/?p=6 kernel softraid (md) beats fakeraid (dmraid) on performance.
> 
> 

 

This is true because most "bios raid" are not real hardware raid and thus use software to manage the arrays.

 *dirk_salewski wrote:*   

> 
> 
> if your mobo dies you need another mobo with same chip (say ICHxR) to get access to your data, whereas md would (in theory) allow to move on to a different mobo without problems

 

Linux Software RAID array are compatible on any motherboard regardless of what controller they have, as all you need is a kernel with Device Mapper and RAID support and you'll be able to start your arrays on the new system. With "bios raid" you're stuck on the particular controller and motherboard it was created.

 *dirk_salewski wrote:*   

> afaik at least ICHxR in RAID mode shows up as normal ahci controller unless using dmraid, without losing functions like ncq and the like[/list]
> 
> Wouldn't it be possible then to use the bios raid functions for installing a gaming windows raid0 (when it dies, it dies, so what), and access the free rest of the disks just normally, to build a "real" kernel softraid on it? 
> 
> Can anybody confirm point three, and did anyone try this? If it works I'd probably buy a ICH9R-based board, if not I'd probably go with a (cheaper) non-raid ICH9-model. 
> ...

 

I can confirm point three but your next point won't work because when you create your arrays on "bios raid" motherboards it will not give you the chance to create a normal linux software raid because the partitions space will be allocated for use with the "bios raid". It doesn't create partitions of desire size on each drive so that you're able to create normal non-raid partitions since it takes up all available space. If you can get a motherboard that doesn't support software raid but if you can't just don't use it and stick with linux raid mdadm.

likewhoa

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## monsm

Yes, agree, think you are stuck with using dmraid if you want to have both windows and Linux on the same raid set.

You could of course get an additional little windows gaming hd, or better still, stick with Linux games.  You'll have to forget about the latest games from the big vendors, but there are still a decent amount of good games for Linux (there are some threads on that here somewhere). A lot will run under wine too, if you know how to configure the ting (bit of a beast if you ask me).

I wouldn't worry about the mobo dyeing.  Unless you are overclocking or stab your screwdriver through it, the chances are very small. I have been running the same raid-0 set using dmraid for about 5 years now.  No problems, touch wood.  I try to take backup on dvd-rw though.

The weak point will be the harddrives themselves, not the mobo. When i set up my machine, I run a full surface scan and tests on the hard drives, to make sure they where ok.  I might check one of these days to see if I can find some number on MTBF (mean time between failure) for my drives.  Although harddrives tend not to break unless they are already damaged when you install them, or if the machine gets moved around too much, they will break after enough usage. Hopefully I get around to upgrade my old AMD +3200 machine before anything goes seriously wrong.

Here's my set of rules: Get good quality hard drives, test them first, be careful if you have to move your machine, take backup of important things like photos, email, music files, other documents you are writing or working on, save-game files   :Wink:   (maybe your /etc tree as well, might save some time if you have to rebuild).

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## dirk_salewski

Thank you for the answers, and that's more or less what I expected. However, I do not *really* want to use win and lin on the same raid set. Those ICH9R-Controllers know a feature called "matrix raid", which allows you to define two different stripesets on a pair of only two disks. I thought that this probably could mean that the bios-fakeraid-controller partitioned the disks, using a partition type of its own, which should then be viewable by cfdisk. If this was the case, I could have defined a bios-based array including only a small PART of each disk (25G each, say). What I would expect to see with linux then would be cfdisk /dev/sda (or sdb) to give: 

1: [strange partition type used by controller], 25Gig, primary partition   (=>sda1, sdb1)

2: large unallocated space   (=>sda2, sdb2)

OR

1: [strange partition type used by controller], 25Gig, primary partition       (=>sda1, sdb1)

2: [strange partition type used by controller], 475Gig, primary partition     (=>sda2, sdb2, so far not used by controller)

Since I don't care about the data on that windows fake-raid partitions (sda1 and sdb1) I wouldn't bother to try reading it from within linux and instead just use cfdisk to create more partitions in the non-used area, which I could then use with mdadm. I wouldn't even install dmraid then.

 *monsm wrote:*   

> You could of course get an additional little windows gaming hd, or better still, stick with Linux games. You'll have to forget about the latest games from the big vendors, but there are still a decent amount of good games for Linux (there are some threads on that here somewhere). A lot will run under wine too, if you know how to configure the ting (bit of a beast if you ask me).

 

I do not really care too much about the latest games - I'm just an Empire Earth I+II and Age of Empires series addict, which I play with my friends (250km away) over internet. Of course I do not really need hardware raid0 on windows to play a 10 year old game. But for me it's like this: if I know functionality is THERE I obsessively try to make it work. Wine doesn't work for EE nor AoE, I tried (no networking, at least). 

 *likewhoa wrote:*   

> I can confirm point three but your next point won't work because when you create your arrays on "bios raid" motherboards it will not give you the chance to create a normal linux software raid because the partitions space will be allocated for use with the "bios raid".

 

Does this apply to these matrix type controllers as well? Even if I give order to the "controller" just to include the first 25Gigs of each disk? 

DS

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## monsm

 *dirk_salewski wrote:*   

> But for me it's like this: if I know functionality is THERE I obsessively try to make it work.

 

Yes, can certainly understand that.  That's pretty much why I set up mine as well.

I googled a bit on that ICH9R chip set.  Does sound from others like it is software raid still.  That matrix stuff is new to me though.  I haven't found anyone in my quick search just now who have tried it like you propose.

It might work though.  At least if Windows is capable of seeing one raid set and leaving the other alone.  It would hopefully see them as 2 hard drives (each of the two sets).

I would think Linux would handle it.  It would see both the individual physical drives as well as both raid sets when you install.  Trick is to choose the raid set you want it to install to (and put grub at the correct place).

I think the true hardware raid is out there, but too expensive still (haven't check recently though).  So I guess it just a matter of getting the best chipset with Linux support and see what happens   :Smile: 

Actually checking that performance test in your initial post, I am not sure it is a valid result.  They are different chipsets and different hard drives on the 2 boxes.  As the guy says, 99% are fake raid (and both in that example).  And in his test both chip sets can either be used in Linux through the bios firmware using dmraid or through the Linux kernel.  The difference is likely to be minimal since in either case most of the work is done in the CPU (true hardware raid has a controller that off-load some work from the CPU). In that blog, most of the difference is likely to be caused by the difference in hardware setup.

So if for some reason the matrix stuff doesn't work out, using dmraid won't make any difference. Maybe other tests on that has a better setup to show any difference (?)

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## dirk_salewski

 *monsm wrote:*   

> They are different chipsets and different hard drives on the 2 boxes.

 

Guess what - I completely jumped over the section describing the hardware, assuming that nobody would try to make a performance comparison between two drivers without making sure that all other factors are kept equal. That's like putting my grandma into adidas, myself into nike and then claim after 100m that nike somehow makes faster shoes. Since this is the only source of comparison I found I'll probably have to check myself and see. 

 *monsm wrote:*   

> I think the true hardware raid is out there, but too expensive still (haven't check recently though).

 

It is not really cheap, but on the other hand not as expensive as one might think. The 3ware 9650SE-2LP SATA-II-Controller for two Harddisks e.g. is as expensive as two 80G-drives together (2008-02-07). Its four-channel brother 9650SE-4LP is available for 1 1/2 that price. 

The problem with those is that they as well do not allow for a combination of RAID 0 and 1 on only two disks. What I really would like to see is something like intels matrix raid, but in that entry level (2LP) hardware raid controller (because you are right, of course: that ICH9R is a softraid chip). 

Greetings, 

Dirk

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