mdadm - raid device name changed on reboot

ARRAY /dev/md/ip-10-0-1-21:0 metadata=1.2 name=ip-10-0-1-21:0 ...

Software RAIDs have a value with a newer superblock have a volume naming scheme beyond just the /dev/mdN. They include a name component that is homehost:volname. This makes it easier to disconnect an array and re-attache it to another system without conflicts.

If udev is setup properly there should be a device named /dev/md/ip-10-0-1-21:0, that is what you should be using in your /etc/fstab for newer style arrays. This device is created for each array when they are running. The /dev/md127 entry is just providing a name for older tools and methods to also be able to use the array. You generally should not be using that name for your mount point, since those names are dynamically allocated during startup. If you add another array tomorrow the device named /dev/md127, might be /dev/md126 instead.