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I would like to know how mdadm identifies physical disks of raid1 .

I think it is managed by uuids not device file like /dev/sdc2 /dev/sdd2.

But I can`t confirm such information of raid1.

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Each Linux RAID volume (RAID-1 or otherwise) contains a superblock which, amongst other things, contains a UUID that is common between all the physical volumes underlying one array, and which is different from the UUID of any other array. For dissymmetric RAID arrangements (i.e. all but RAID-1), the volumes also contain information that tell mdadm which is which. When you tell mdadm to assemble an array, it looks for physical volumes which have the same UUID. You can tell it which physical volumes to look in, otherwise mdadm will scan your system; but the location of the physical volume (e.g. /dev/sdc2 vs /dev/sdd2) is irrelevant, only the UUID.

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