First questions

The very first thing you are asked to select is the language you want to use for the installation process (which will subsequently be set as default language for the installed system): choose English, if you share my preferences. After that, you have to choose your country, so that the correct timezone will be set: select other, Europe, then Italy (or otherwise, if you live elsewhere...). On next screen, choose the locale: select "en_US.UTF-8". Then choose the keymap to use: select "American English", if you have a US keyboard.

The installer says that some of your hardware (one onboard network interface) needs non-free firmware and offer to load it from removable media: you may proceed without it (select "No").

At that point the installer warns that multiple network interfaces were found in the system and ask the user to choose the primary interface. One is the Intel I218-V, the other one is the Realtek RTL8111/8168/8411: choose Intel as primary interface (assuming that you connected this interface to your LAN). The installer then proceeds to configure the network through DHCP. If you have a DHCP server on your LAN (as in my case), it succeeds and no further configuration is needed.

Now, use your creativity and choose a hostname for your box! You have to enter one in the next screen. Hereinafter, I'll refer to the chosen hostname as $HOSTNAME. Then, you have to enter the domain name: leave the field blank, if you have no established domain name for your LAN.

Time to set the root password: try and think a good one! You can create a regular user as well: enter your full name, a username, and a password.

Partitioning the disk

The goal is setting up a (hopefully) good partitioning layout for a workstation usage, with the two SSD drives in software RAID1. When asked, choose the manual partitioning method. Next screen displays the current partition tables:

SCSI1 (0,0,0) (sda) - 250.1 GB ATA Samsung SSD 850
SCSI2 (0,0,0) (sdb) - 250.1 GB ATA Samsung SSD 850

The USB stick is also displayed, but should obviously be left untouched.

Select the first drive (sda) and answer "Yes" when asked whether a new partition table should be created. Select the free space line and choose "Create a new partition" from the dialog screen. Enter "540 MB" as partition size and create the partition at the beginning of the available space, change the "Use as" entry to "EFI System Partition". After choosing "Done setting up the partition", you get back to the partition table screen, with the following updated status:

SCSI1 (0,0,0) (sda) - 250.1 GB ATA Samsung SSD 850
             1.0 MB        FREE SPACE
     #1    539.0 MB  B  f  ESP
           249.5 GB        FREE SPACE
SCSI2 (0,0,0) (sdb) - 250.1 GB ATA Samsung SSD 850

Again select the big free space line and choose "Create a new partition". Enter "1.5 GB" as partition size and create the partition at the beginning. Change the "Use as" entry to "physical volume for RAID". After choosing "Done setting up the partition", you get back to the partition table screen, with the following updated status:

SCSI1 (0,0,0) (sda) - 250.1 GB ATA Samsung SSD 850
             1.0 MB        FREE SPACE
     #1    539.0 MB  B  f  ESP
     #2      1.5 GB     K  raid
           248.0 GB        FREE SPACE
SCSI2 (0,0,0) (sdb) - 250.1 GB ATA Samsung SSD 850

Go on setting up partitions according to the following table:

entered size	use as
"9.0 GB"	swap
"24.0 GB"	raid
"14.0 GB"	raid
"900 MB"	raid
"max"	raid

Back to the partition table screen, the situation should look like:

SCSI1 (0,0,0) (sda) - 250.1 GB ATA Samsung SSD 850
             1.0 MB        FREE SPACE
     #1    539.0 MB  B  f  ESP
     #2      1.5 GB     K  raid
     #3      9.0 GB     f  swap          swap
     #4     24.0 GB     K  raid
     #5     14.0 GB     K  raid
     #6    899.7 MB     K  raid
     #7    200.1 GB     K  raid
           171.5 kB        FREE SPACE
SCSI2 (0,0,0) (sdb) - 250.1 GB ATA Samsung SSD 850

Now select the second drive (sdb) and create an identical partition table. After doing so, choose "Configure software RAID". You'll be asked to confirm the creation of partitions, before you can proceed: answer "Yes".

The next screen allows you to configure software RAID: choose "Create MD device", select "RAID1", with "2" active devices and "0" spare devices. Select "/dev/sda2" and "/dev/sdb2". Repeat this procedure to create other MD devices by coupling the other twin physical volumes for RAID. Choose "Finish", when you're done with MD device creation.

In the partition table screen, select the "#1 1.5 GB" line: change the "Use as" entry to "Ext4 journaling file system", and the mount point to /. After choosing "Done setting up the partition", repeat the process for the other MD devices, until the result is as follows:

RAID1 device #0 - 1.5 GB Software RAID device
     #1      1.5 GB     f  ext4          /
RAID1 device #1 - 24.0 GB Software RAID device
     #1     24.0 GB     f  ext4          /usr
RAID1 device #2 - 14.0 GB Software RAID device
     #1     14.0 GB     f  ext4          /var
RAID1 device #3 - 899.1 MB Software RAID device
     #1    899.1 MB     f  ext4          /tmp
RAID1 device #4 - 200.0 GB Software RAID device
     #1    200.0 GB     f  ext4          /home
SCSI1 (0,0,0) (sda) - 250.1 GB ATA Samsung SSD 850
             1.0 MB        FREE SPACE
     #1    539.0 MB  B  F  ESP
     #2      1.5 GB     K  raid
     #3      9.0 GB     F  swap          swap
     #4     24.0 GB     K  raid
     #5     14.0 GB     K  raid
     #6    899.7 MB     K  raid
     #7    200.1 GB     K  raid
           171.5 kB        FREE SPACE
SCSI2 (0,0,0) (sdb) - 250.1 GB ATA Samsung SSD 850
             1.0 MB        FREE SPACE
     #1    539.0 MB  B  F  ESP
     #2      1.5 GB     K  raid
     #3      9.0 GB     F  swap          swap
     #4     24.0 GB     K  raid
     #5     14.0 GB     K  raid
     #6    899.7 MB     K  raid
     #7    200.1 GB     K  raid
           171.5 kB        FREE SPACE

Choose "Finish partitioning and write changes to disk"; you'll be asked to confirm the creation of the partitions: answer "Yes". The desired filesystems are created.

Finishing the installation

At this point, you just have to wait for the base system to be installed. Then you'll be asked to choose a mirror near you (for instance choose Italy, deb.debian.org, which is the Debian CDN). You also have to specify an HTTP proxy, if you use one; if instead you do not use any HTTP proxy on your LAN (as in my case), then leave the proxy field blank. Then you'll be asked whether you want to contribute to popcon: answer "Yes", if you care about Debian. The next screen allows you to select groups of packages: since the goal here is installing the base system only, deselect everything and choose "Continue".

The installation is complete: remove the USB stick and choose "Continue" to reboot the system!

Configuring the boot process for failing drives

In order for the RAID1 setup to be really useful, the system must be able to boot even when one of the two drives fails to work correctly.

To this aim, we have to add the "nofail" option to the swap partitions and to the EFI system partition (ESP) in /etc/fstab:

# grep nofail /etc/fstab
UUID=CE67-C4AD  /boot/efi       vfat    umask=0077,nofail     0      1
UUID=f5c29a-d648 none       swap    sw,nofail     0      0
UUID=8eecee-6d08 none       swap    sw,nofail     0      0

Moreover, we can use the EFI system partition (ESP) created on the second drive (sdb). Since the first ESP is mounted on /boot/efi, we can mount the second ESP on /boot/efi2. First of all, create the mount point:

# mkdir /boot/efi2

Then, figure out the UUID of the second ESP:

# blkid /dev/sdb1

add a corresponding entry to /etc/fstab:

# grep efi2 /etc/fstab
# /boot/efi2 was on /dev/sdb1 during installation
UUID=CE67-EBDD  /boot/efi2      vfat    umask=0077,nofail     0      1

and mount the second ESP:

# mount /boot/efi2

Finally, copy the content of /boot/efi to /boot/efi2:

# cp -a /boot/efi/EFI /boot/efi2/

At this point the system should become able [1] to boot from any of the two drives. To this aim, configure the UEFI boot order so that the machine attempts to boot from the second drive (this way, you can check that it is actually able to do so) and then from the first one as a fallback:

# efibootmgr
BootCurrent: 0000
Timeout: 1 seconds
BootOrder: 0000
Boot0000* debian
# efibootmgr --create --disk /dev/sdb --loader '\EFI\debian\grubx64.efi' \
  --label debian2 --part 1
BootCurrent: 0000
Timeout: 1 seconds
BootOrder: 0001,0000
Boot0000* debian
Boot0001* debian2

If the efibootmgr command is not available, install the corresponding package:

# apt update && apt install efibootmgr

Please note that /boot/efi2 has to be manually kept in sync with /boot/efi: update it whenever the content of /boot/efi changes (that is to say, whenever package grub-efi-amd64 is upgraded). Moreover, the EFI boot order configuration has to be set again (whenever package grub-efi-amd64 is upgraded).

[1]	currently this requires manual intervention on the console: see bug #784070 for further details

Optimizing the SSD performance

Since the drives are SSDs, it is suggested to enable TRIM support at filesystem level. It will transparently pass through the software RAID layer.

Edit file /etc/fstab, adding the "discard" option to each ext4 filesystem (for instance "defaults" becomes "defaults,discard") and even to the vfat and swap partitions.