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I'm testing out sw raid in windows 7, but I almost always use linux and I would like to know if it's possible to mount such a mirrored dynamic disk.

I can already mount each members separatly but accessing both of them at the same time would keep it consistent!

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I'd be doubtful –  mdpc Jan 8 '13 at 19:49
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2 Answers

Without trying it yet (I'm aiming for a similar setup in the future): it should be possible to create an MD device with mdadm --build, which should just create a plain raid without any kind of superblock - see the man page for details. I would strongly suggest trying out first on a couple of loop devices (see man losetup) to make sure it works: put two or more loop devices in an MD RAID and keep two copies of the initial content for reference, do arbitrary data changes to the MD and one reference copy, disassemble the MD device, compare the MD members and the reference copy. Repeat a reasonable number of times. If it fails, compare with the untouched reference to see where are the differences and submit a bug report.

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I have used mdadm extensively for years now and I can tell you it works just fine. The question is how to access microsoft version of software raid, from linux. –  bksunday Jan 8 '13 at 23:55
I would expect it to just mirror the data - i.e. if you can mount the single devices, creating MD from them should be enough. You can check whether the devices have the same content by comparing them prior to doing any experiments. If they are the same indeed I'd say give it a try. If not, check what the differences are - you might be lucky enough to be able to tell that it's e.g. partition UUID. –  peterph Jan 9 '13 at 15:46
I had to re-read you a couple of times to fully understand what I had to do from your answer & comment. I can mount each single member of a ms dynamic disk and haven't tried building an array out of them without writing superblocks.. It actually sounds promessing! I just wish I could create the test disks from lvm ;) ... And I can't vote up your answer.. –  bksunday Jun 3 '13 at 2:26
Well, if you have a couple of GB of free space (~50GB+) you can install Windows in a virtual machine and try it - it shouldn't take more than 2-3 hours (third of which you'll probably spend waiting for automated tasks like the installation to finish). –  peterph Jun 3 '13 at 13:23
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The short answer is no. The dynamic disks format has been partially reverse engineered and support for mapping simple volumes ( partitions ) has been added to the kernel, but that's about it.

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Ms dynamic disk was probably reverse engineered from mdadm and alike wouldn't you say? I also wanted to vote up your answer but I'm too low on points (1) ;). And the partial reverse engineering was enough to let me mount each array members! :) –  bksunday Jun 3 '13 at 3:09
@bksunday, mdadm has nothing to do with it. If you mount half of the mirror and make any changes to it, then you will corrupt the filesystem when Windows mounts it again. –  psusi Jun 3 '13 at 13:48
Yes. I mount the members read-only in order to avoid corrupting the fs. –  bksunday Jun 3 '13 at 16:51
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