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Originally md device files were /dev/md[[:digit:]]+.  Now /dev/md/[[:digit:]]+ is preferred.

Andrey reports that having auto-generated /dev/md/* names in mdadm.conf breaks GRUB or initramfs in recent (Trusty and Jessie) systems.  TODO: clarify (including adding related bug references) and determine whether our policy should be to defend against such auto-generated names or whether this is a transient situation which will be bug-passed.

RAID 1

Creation

Create the block devices to be used as underlying devices.  Typically these are HDD partitions but any block devices can be used.  In the following example, /dev/sdb1 /dev/sdc1 are used.

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