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.  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 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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