Clean OS (Debian), OpenMediaVault and other "firmwares"

[amix]

Hello,

I purchased a gen2 My Cloud single bay 4TB a few days ago. It is still in its virgin state, I did not configure anything except passwords and SSH access. I decided I want to install OMV on it, maybe also NextCloud and Omeka, along with TimeMachine and other backups (should the memory allow for it). This means, I might need to install a full Linux on it. But before I do, I would like to make sure, that I understood the architecture of the device. I would be very glad, if somebody could comment on this, or even better, walk me through the device architecture and the available options.

As I see it, the gen2 My Cloud device looks like this:

• Marvell Armada 375 (ARMv7, dual core, 32bit, Linux armhf architecture)
• 512MB RAM
• 256MB Flash Rom
• 4 TB HDD
• 1Gbit/s (model unknown to me, I guess it will be from Marvell as part of the SOC)

Disk layout, after boot, is:

root@WDMyCloud /etc # blkid -o list
device                         fs_type             label       mount point                        
--------------------------------------------------------------------------------------
/dev/loop0                     squashfs                        /usr/local/modules
/dev/sda1                      linux_raid_member               (in use)       
/dev/sda2                      ext4                            /mnt/HD/HD_a2
/dev/sda3                      ext4                            /boot
/dev/sda4                      ext4                            /mnt/HD_a4
/dev/sda5                      ext4                            (not mounted)
/dev/sda6                      ext4                            (not mounted)
/dev/sda7                      ext4                            /usr/local/config
/dev/md0                       swap                            <swap>

So, /dev/sda[1-7] are partitions on the internal 4TB HDD.

• I understand, that the data partition (the NAS as exposed to the users on the network) is /dev/sda2.
  What are the other partitions (except /dev/sda3, that contains the boot images) good for?

• Especially, what is with /dev/sda5 and /dev/sda6? Both are ‘not mounted’ but consume each 1GB of capacity.

• Where is the bootloader located? I mean, physically. Is it on the MBR of /dev/sda or is it on the flash-disk?

• Is LILO in use? Not sure, how this is on embedded devices. I read, that U-Boot combines stage 1 and stage 2.

• /dev/md0 seems to be physically located at /dev/sda1, which as a Linux swap filesystem and is mounted as a RAID1 device, consisting of a single partition. I wonder why they did it this way, rather than just having an ordinary swap partition.

• Is /dev/loop0 a Ram Disk? Or is it on the internal flash?

As to what I understand, so far,

• there is a bootstrap environment, U-Boot, that handles the boot. I assume U-Boot must reside in the system’s flash disk? According to IBM Developer Work’s “Inside the Linux boot process” booting on an embedded device differs from booting on a PC. How does the boot process happen on the factory firmware? Does it happen differently on the CleanOS or Alpine firmware? I would be interested in information, as to where what is.

• When I install CleanOS or Alpine, will it overwrite the original firmware? (I am going to install Debian, since I want OMV, but, out of curiosity, I would be interested, how the Alpine mod has been engineered as well.

• How do I remake a modified system into it’s virgin, factory-delivered state?

Currently I like the fact very much, that the data disk does not spin up, when I use the web-admin or the do maintenance via SSH. There seems to be some “lobby” in a RAM Disk or on Flash. Will this be the same, if I install @Fox_exe’s Debian?