Access RAID1 content from other Linux system of a dual boot

I have prepared for a friend a little NAS made of Ubuntu Server 20.04 on an SSD and two HHD in RAID1.

The software RAID1 has been made during the Ubuntu installation, here some info about it:

$ fdisk -l
Disk /dev/sda: 3.65 TiB, 4000787030016 bytes, 7814037168 sectors
Disk model: WDC WD40EFRX-68N
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes

Disk /dev/sdb: 3.65 TiB, 4000787030016 bytes, 7814037168 sectors
Disk model: ST4000VN008-2DR1
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes

Disk /dev/md1: 3.65 TiB, 4000651739136 bytes, 7813772928 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes

(I was expecting to see partitions here, but there seems to be no sda1 or sdb1...)

$ cat /proc/mdstat
Personalities : [raid1] [linear] [multipath] [raid0] [raid6] [raid5]
[raid4] [raid10]  md1 : active raid1 sdb[1] sda[0]
      3906886464 blocks super 1.2 [2/2] [UU]
      bitmap: 0/30 pages [0KB], 65536KB chunk

unused devices: <none>

My friend is going to connect and transfer files to it with WinSCP from his Windows computer. I still have to install Jellyfin so that he can browse his media easily.

Till here everything is ok!

But as my friend does not know anything about Linux and network as well, I am thinking of an option that could let him access the files on the RAID1 in case of a problem. Like if something prevent him from reaching the server from his Windows computer, if the RAID1 failed somehow or if I am not here to help.

So I ended up installing Linux Mint on a another partition of the SSD, so that he can boot to it in case of emergency, thanks to a dual boot option in Grub.

In order to access his content from Linux Mint, I see two options:

1. re-creating the RAID1
2. allow access to each drive of the RAID1 (/dev/sda and /dev/sdb)

Options 1) should be easily done by activating the RAID1 with mdadm --assemble --scan and then mount /dev/md1

I did not try that though, because in case of a RAID problem, I think it should be safer to be able accessing each member of the RAID separately.

That's where I am stuck...

I have tried adding the /dev/sda UUID in fstab

/dev/sda 3.7GB  UUID=xxx /mnt/local_disk1 ext4    errors=remount-ro 0       1

and then mount it with mount /mnt/local_disk1 /dev/sda, but this is what I get:

mount: /mnt/local_disk1 : wrong fs type, bad option, bad superblock on /dev/sdb, missing codepage or helper program, or other error.

I also tried to specify the file system with mount -t ext4 /mnt/local_disk1 /dev/sda, which gives me:

mount: /dev/sda : /mnt/local_disk1 is not a block device

Any idea of what I should do to let me access the content of /dev/sda from Linux Mint? (Obviously without breaking the RAID1 of Ubuntu server ;)