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Thinking in terms of the future, let's say I buy 4 external disks, set them up with Ubuntu Server 12.04 software RAID 1+0. Then later after some usage I want to stick them on a new computer - how do I ensure they work immediately?

If I just plug them into the fresh computer (with any other hard disks removed), will they automatically know how to relate to each other REGARDLESS of which order of external slots I plug them into? Or do I have to be careful to plug them in a certain port order?

If neither of these are guaranteed to work, then what steps must I take to ensure I get the Ubuntu booting up and running with the software RAID 1+0 exactly as before, bearing in mind I'm relatively new to Ubuntu Server?

And does it matter if I use any combination of external ports for the drives (e.g. USB 2.0, 3.0, eSATA 2.0, 3.0, any future versions of USB, eSATA etc.)?

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Do you have a separate boot volume? I haven't tried with 12.04, but I don't believe that previous LTS will support booting to a RAID10 volume. – Zoredache Jul 6 '12 at 18:54
up vote 1 down vote accepted

Yes, they'll all work fine because the MD superblock contains a UUID identifying the drives as all belonging to the same RAID volume. When you tell mdadm to auto-assemble, it scans all block devices and will find the MD superblocks and put the volume back together again.

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Do I have to tell mdadm to auto-assemble manually, or is this automatic when I plug them all in and switch on the new computer? If it's manual, what do I type? – Navigateur Jul 6 '12 at 18:58
That one depends on an awful lot of factors, including how the initrd you boot from is configured, how precisely you boot the system, and what hardware you've got. So the only answer I can give is "try it and find out". To assemble RAID sets auto-manually, run mdadm --auto-detect. – womble Jul 6 '12 at 19:05

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