On 01/02/12 10:58, Anton Cohen wrote:
> BIOS RAID is usually FakeRAID. There is no hardware RAID controller,
> just a normal SATA controller. The BIOS does some magic during boot,
> once the OS loads the RAID functionality is performed by a special OS
> driver and the CPU, just like software RAID is done by the kernel
> [module] and CPU. So BIOS RAID is software RAID.
>
> http://en.wikipedia.org/wiki/RAID#Firmware.2Fdriver-based_RAID
> https://help.ubuntu.com/community/FakeRaidHowto
>
> Windows 7 can do mirroring:
> http://buildegg.com/bewp/?p=44
>
> -Anton
My experience (circa 2009), FakeRAID (aka. dmraid in Linux) is something
to stay away from when running Linux. There is no way to rebuild a
degraded dmraid. In fact, I had a mirrored boot drive where we had a
failure in one of the drives, the BIOS booted the other drive fine, but
the kernel failed to piece together the degraded RAID and ended up with
no boot drive.[*]
What I had found was I would have to put together a Windows system with
the same motherboard type and connect the drives to it. Then have the
full RAID implementation in the Windows drivers do the rebuild.
This option is really only there to make dual booting Windows/Linux with
a really cheap RAID possible.
Oh, and the RAID settings are not in the BIOS. All FakeRAID drives have
a signature written to them (at the end of the disk). There are
multiple formats for this signature, depending on the FakeRAID
manufacture. dmraid supports a bunch of signatures. These signatures
contain all of the metadata.
In my experience, I pretty much stick to real hardware RAID for boot
drives, then data drives are optional with MD or real hardware RAID systems.
My home fileserver runs MD in a RAID10 for the data drives.
$ cat /proc/mdstat
Personalities : [raid10]
md0 : active raid10 sdd1[2] sde1[3] sdb1[0] sdc1[1]
5860527744 blocks super 1.2 64K chunks 2 near-copies [4/4] [UUUU]
For Windows systems, FakeRAID should work ok. But, I would still stick
with the same recommendation of hardware RAID for boot drives for
Windows systems.
Windows has it's own LVM system (dynamic drives) that support mirroring.
This can be used in place of MD on Windows systems.
* The 2 year old startup I had joined was selling Linux based appliances
touting mirrored drives, though they never tested a degraded mirror. So
I showed them, by pulling one drive. It ran fine, until it was
shutdown. There was no way to get it booted again.
--
END OF LINE
-MCP
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