ref: https://askubuntu.com/questions/1234949/install-ubuntu-20-04-focal-fossa-with-raid-1-on-two-devices
This is for manually configuring software RAID1 for two disks. This can be useful for isolating your boot drive from your storage RAID pool, but still ensuring redundancy, without the need for chipset specific software/mobo RAID or a secondary RAID controller.
when installing ubuntu server, follow through the prompts until you reach the 'storage configuration' step, then select 'custom storage layout'.
- reformat both drives.
to avoid confusion, we'll call the disks 'disk1' and 'disk2', this does not literally mean that is what they will be labeled on your machine. apply the following steps accordingly to what your first and second disk in the RAID1 array are actually called.
there should be 2x 1mb bios grub partitions. if this does not exist under secondary, you can manually create a 1mb partition so the other partitions align. 2 grub partitions are not necessary.
- add 1gb GPT partition on disk1, leave unformatted, repeat for disk2.
under each disk on available devices, you will now see 'partition 2', this is for boot.
- add 16gb (or whatever half your RAM size is) GPT partition on disk1 and leave it unformatted. repeat for disk2.
you will now see 'partition 3'. this is for swap.
- add GPT partition to disk1 (do not set a size) and leave it unformatted. repeat for disk2.
you will now see 'partition 4'. this is for root.
- choose 'create software RAID (md)' under 'available devices'.
- create md0 by selecting 'partition 2' from both disk1 and disk2, choose save.
- repeat for md1 and both 'partition 3'. save.
- and gain for md2 and both 'partition 4'. save.
there should now be 3 pairs of available devices.
- select md0 and 'add GPT partition', format as EXT4 and mount on /boot.
- select md1 and 'add GPT partition', format as SWAP
- select md2 and 'add GPT partition', format as EXT4 and mount on /.
these should now appear under 'used devices'
you can now continue with the ubuntu installation
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