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Normally, I create RAID arrays during installation, but I'm trying to add an array to an existing system. The OS (Mint16) is on its own drive. I've added two brand new physical drives to the machine, and I want to create a RAID 1 array out of them.

When I used the installer, there was an option to make a partition a "physical volume for software RAID". There is no such option in fdisk or Gparted, so far as I can tell.

fdisk also complains that The device presents a logical sector size that is smaller than the physical sector size. So whatever partition came on the drive is less than optimal.

What command should I run on the drives (they are empty and have no data) to create a full drive partition with the right sector size, in preparation for them to be used as a RAID members?

I feel like there's some step that should be run before the mdadm --create step that preps them to be RAID members and fixes the sector size issues.

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You don't actually need to partition a drive if you want to add it in its entirety to a RAID device; you can specify the whole device (/dev/disk/by-uuid/...) as a component for mdadm.

If you still want to use a partition, run wipefs -a on the device, and create the partition with a recent version of cfdisk or parted; they will do the right thing as far as partition alignment is concerned. For RAID auto-detection the partition type to use is 0xFD (I think it's not longer necessary to use that partition type but it makes the partition table easier to understand).

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