Re: [gentoo-user] Software RAID Advice Needed

[Jim Burwell <jimb@jsbc.cc>]

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Richard Fish wrote:

>On 12/15/05, Ognjen Bezanov <ognjen@mailshack.com> wrote:
>  
>
>>I have found Linux Software RAID very useful and reliable. While
>>probably being beaten in the performance  area by hardware
>>implementations,
>>    
>>
>
>I just want to point out that when we are talking hardware here, we
>mean real hardware RAID...made by companies like 3-ware.  The
>'hardware' RAID in the NForce4 chipset (like just about all MB chips,
>and a lot of the cheap add-in cards) is just a BIOS helper...all of
>the actual RAID functions are expected to be implemented by the driver
>running on the CPU.
>
>  
>
Don't you hate how the hardware and mobo manufacturers have muddied the 
hardware RAID waters by marketing this sort of thing has hardware RAID 
(or at least implying it) ?

Another thing to check out, seeing that he has a mobo with built in 
ghetto-RAID (TM), is dmraid 
<http://people.redhat.com/%7Eheinzm/sw/dmraid/readme>.  This is a device 
mapper implementation of RAID which makes use of various fake hardware 
RAID metadata to support them under Linux.  Someone's also done up a 
Gentoo LiveCD <http://tienstra4.flatnet.tudelft.nl/%7Egerte/gen2dmraid/> 
with dmraid support on it too (who knows, perhaps the latest liveCDs 
have it also).  The only advantage of using this I can see is the 
ability to to make use of the BIOS RAID helpers to create and manage 
your arrays, and deal with the inherent boot time issues.  I'm not sure 
about the stability or reliability of this though, as I havn't used it, 
and the readme doesn't really give me courage :-).  Anyone using this 
successfuly ?  It seems interesting.

I just put together a little home server which uses both Linux RAID (md) 
and LVM2 on an old Abit KG7-RAID motherboard.  Even though it has a 
built in Highpoint HPT37X "RAID chip" (a ghetto-RAID BIOS helper), I 
decided to go with good old "md".  I've tested it by pulling power on 
drives, and it even boots up when the 'primary' drive doesn't exist 
(boot blocks on both mirrored drives of course).  Seems to work very 
well.  I have /boot mirrored (md0), and root and swap on LVM2 partitions 
which live on another mirrored partition (md1). 

For any wanting to do similar, you just need to set up GRUB on both 
drives, and make sure your have initramfs support for starting up md and 
LVM2.  Generkernel will produce a kernel with this if you compile the md 
drivers into the kernel, and include --lvm2 in the genkernel flags.  
Make sure you include "dovlm2" and lvmraid=/dev/mdX lines for each of of 
your RAID devices on the boot line, which tells the linuxrc scripts to 
start up your RAID devices in the initramfs so it can mount your LVM2 
root partition.

- Jim

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