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I have a fake raid, which I wanted to access using

mdadm /dev/md0 -A -c 128 -l stripe --verbose /dev/sda /dev/sdc

which should be right, as far as I understand the man page. But I get the message

mdadm: option -l not valid in assemble mode

leaving the offending option out leads to

mdadm: failed to create /dev/md0

and (despite verbose) no more information. I'm assuming that -A requires some mdadm-specific header which is obviously missing. I probably need to use "build" instead of assemble, but from the description I'm really unsure whether this is a non-destructive operation. Is it? What should I exactly do?


I see I haven't made clear, that the array already exists as a fake-raid (I can't give the details about my mainboard now). It looks like doing nothing except for interleaving blocks, so I hoped it could be easily done using mdadm, too. Maybe I'm completely wrong, but all the info I've found was concerned with booting from fake-raid, what I don't really need. I'd be happy with a read access for now.


The solution from the answer nearly works. My fake-raid gets recognized by dmraid, but it refuses to start because of missing disks. I've forgotten to mention that my RAID10 is running without two disks i.e. it's just stripped. (I've already moved the important data to a safer place).

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This isn't "fake raid", this is "software raid". FakeRAID uses semi-hardware controllers that offload their processing onto the CPU and use a driver called dmraid. Could you update your post accordingly, please? – Oli Mar 4 '11 at 15:51
If this is fakeraid, your only real option is to use the controller the data was written there with. dmraid should pick up the controller and automatically make a mapping to a virtual device in /dev/mapper/ that you can mount. If you're trying to mount two fakeraid disks on another system, you're probably out of luck. fakeraid is painfully unmoveable. – Oli Mar 4 '11 at 17:05
up vote 3 down vote accepted

Fake raid is accessed with the dmraid utility, not mdadm. It should also work out of the box with recent Ubuntu releases. See for more information, though much of the how to part does not apply with recent releases, since as I said, it now just works automatically.

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