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I have two GPT formatted disks both starting with EFI partitions and followed by a single physical raid partition. I installed ubuntu-server 16.04 with software raid over these two raid partitions and once it had installed, I cloned the EFI partition from the mounted EFI partition to the unmounted one using dd if=/dev/sda1 of=/dev/sdb1 and then inserted the second disk into the UEFI boot chain using sudo efibootmgr -c -d /dev/sdb -p 1 -L "ubuntu2" -l '\EFI\ubuntu\shimx64.efi' so that if a disk broke I would still be able to boot from the other disk.

At some point I did apt upgrade and noted that grub was updated so I checked which EFI partition was mounted and cloned it to the other using the same dd command as earlier and then rebooted and checked the output of efibootmgr.

I notice that both HD boot entries begin with "ubuntu HD(1, ....". but I was expecting one of them to begin with "ubuntu2" (and maybe "HD(2, ..." ?)

My questions is: What does this output mean? Are these entries both referring to the same disk or to each disk as I expect? To ensure mutual bootability, do I need to delete the entries and then reinsert them as originally?

I'm afraid to shut down the system and remove a disk to test things in case I bring about a lot of downtime by doing something without properly understanding what's going on.

$ sudo efibootmgr -v
BootCurrent: 0001
Timeout: 3 seconds
BootOrder: 0001,0000,2001,2002,2003
Boot0000* ubuntu        HD(1,GPT,ae9a1a9a-1336-4871-a8a8-07cdaf82fc9f,0x800,0xee000)/File(\EFI\ubuntu\shimx64.efi)
Boot0001* ubuntu        HD(1,GPT,9a770a2c-e8b6-4921-ab2c-4153c3efc8ea,0x800,0xee000)/File(\EFI\ubuntu\shimx64.efi)
Boot2001* EFI USB Device        RC
Boot2002* EFI DVD/CDROM RC
Boot2003* EFI Network   RC

$ lsblk
NAME          MAJ:MIN RM  SIZE RO TYPE  MOUNTPOINT
sda             8:0    0  3.7T  0 disk  
├─sda1          8:1    0  476M  0 part  
└─sda2          8:2    0  3.7T  0 part  
  └─md0         9:0    0  3.7T  0 raid1 
    ├─vg-root 252:0    0  3.7T  0 lvm   /
    └─vg-swap 252:1    0 29.8G  0 lvm   [SWAP]
sdb             8:16   0  3.7T  0 disk  
├─sdb1          8:17   0  476M  0 part  /boot/efi
└─sdb2          8:18   0  3.7T  0 part  
  └─md0         9:0    0  3.7T  0 raid1 
    ├─vg-root 252:0    0  3.7T  0 lvm   /
    └─vg-swap 252:1    0 29.8G  0 lvm   [SWAP]
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Worked this out, it is explained and answered in my related question: How can I generate/or edit a grub.cfg on each EFI partition that refers to the ubuntu installation on the same physical disk?

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