fake hardware raid5

[laser-axel]

Hello,

I am trying to mount an existing windows partition with knoppix. The purpose is to make a dump of the windows installation.
There is an Intel 82801 SATA RAID Controller (rev 05) in the system. There are 4 HDs. 3 are arranged as an RAID5 and one is spare. I use knoppix 6.7.1 CD (german).

dmraid -b shows all 4 HDs.
When I try "dmraid -ay" I get 3 errors:

ERROR: spare set "isw_diffiigjfb_/dev/sdd" cannot be activated
ERROR: no mapping possible for RAID set isw_diffiigjfb_/dev/sdd
ERROR: device-mapper target type "raid45" is not in the kernel
RAID set "isw_gcdfjaffh_Volume0" was not activated

The first two belong to the spare device as sdd is the spare device (compared serial numbers in BIOS config and dmraid -b). The third one produces a lot of google-hits and seems to be a well known version/naming issue between dmraid a kernel. But I did not get any Information on how to fix/ work around it.
There is a kernel module called raid456.ko and it is loaded according to lsmod.

[CrazyCasta]

I have two solutions for your issues:

1. You need to be running dmraid version >= 1.0.0-rc16 if you're running kernel >2.6.36. To determine you dmraid version just use

dmraid -v

.
2. If you already have dmraid version >= 1.0.0-rc16 then you need a kernel module for dm-raid45. The kernel module that comes out as raid45.ko is actually an unrelated module for mdraid (linux software fakeraid as opposed to firmware assisted windows compatible software fakeraid which is what dmraid is). You might also notice the device mapper raid456 module, this will eventually be what you want, but as of yet there is no support for it in the userspace tool, so you can't use it (even though it's in the main kernel :P). What you need is the dm-raid45 kernel module. I'm maintaining a patchset at http://code.google.com/p/dmraid-patches/ . You would of course have to compile the kernel yourself. One solution would be to get the kernel source of the version you're running, patch it, make dm-raid45.ko as a module and just throw the rest away. I'm not familiar with building the kernel on knoppix, so best of luck .

[laser-axel]

Thank you for your answer.
There was a lot of work for me in the meantime. The PC is now at customer site. Thus, my abilities to experiment with patched kernels in knoppix are very limited.
The basic message is that I need to learn more about the difference between software mdraid and BIOS-supported-fake-hardware-but-in-the-end-also-software dmraid. Anyway the whole dmraid stuff seems a little unfinished/ awkward to me.

One general question remains. Is this way of retrieving and putting back images really a gain in failure safty compared to the BIOS-supported-fake-hardware-but-in-the-end-also-software RAID5 with hot spare? At the moment I cannot confidently make this statement to a customer.