Points of departure:

• MBR: Master boot record. Grub will install boot.img here, hardware will boot from this. Then it wil load first sector from core.img.
• core.img: Will load its configuration file and any other modules needed, particularly file system drivers. It will load config from /boot/grub
• GPT: GUID partition table.
• BTRFS: file system.
• GRUB2: bootloader
• SystemD: init system.

• Download 64 bit ISO and verification files: http://distfiles.gentoo.org/releases/amd64/current-iso/
• Verify signature:

  gpg --recv-keys 0xBB572E0E2D182910
  gpg --verify install-amd64-minimal-20141204.iso.DIGESTS.asc

• Verify key with: https://www.gentoo.org/proj/en/releng/.
• Verify integrity:

  grep -A 1 -i sha512 install-amd64-minimal-20141204.iso.DIGESTS.asc
  sha512sum install-amd64-minimal-20141204.iso.DIGESTS.asc
  
  #or
  openssl dgst -sha512 install-amd64-minimal-20141204.iso

• Mount ISO via iLO, IPMI, etc…
• Boot server from ISO (F11 on X9SCL/Supermicro).
• Boot Gentoo:

  boot: gentoo

• Select keymap, or leave default.

• Configure networking, for example DHCP:

  dhcpcd enp4s0

• Change root password, create user and start SSHd

  # passwd
  # useradd -m -G users,wheel john 
  # passwd john
  # /etc/init.d/sshd start

• Log in via SSH and switch to root.

• I've played a lot with software RAID, LVM, GPT etc. So lets completely wipe the SSDs. See: secure_wipe
• Create GPT partitions including swap on sda:

  gdisk /dev/sda
  o          #create empty new GUID partition table.
  n          #add new partition.
  1          #partition number 1.
  2048       #default first sector.
  +2MiB      #BIOS boot partition size.
  ef02       #partition type.
  
  n          #add new partition.
  2          #partition number 2.
  <default>  #default next sector.
  +2GiB      #SWAP partition size.
  8200       #partition type.
  
  n          #add new partition.
  3          #partition number 3.
  <default>  #default next sector.
  <default>  #Rest of disk.
  8300       #partition type.
  w          #write changes and exit.

• Create GPT partitions swap on sdb:

  gdisk /dev/sdb
  o          #create empty new GUID partition table.
  n          #add new partition.
  1          #partition number 1.
  2048       #default first sector.
  +2MiB      #BIOS boot partition size.
  ef02       #partition type.
  
  n          #add new partition.
  2          #partition number 2.
  <default>  #default next sector.
  <default>  #Rest of disk.
  8300       #partition type.
  w          #write changes and exit.

• Create RAID1 filesystem:

  # mkfs.btrfs -L btrfsmirror -m raid1 -d raid1 /dev/sda3 /dev/sdb2
  
  WARNING! - Btrfs v3.14.2 IS EXPERIMENTAL
  WARNING! - see http://btrfs.wiki.kernel.org before using
  
  Performing full device TRIM (57.62GiB) ...
  Turning ON incompat feature 'extref': increased hardlink limit per file to 65536
  Performing full device TRIM (59.62GiB) ...
  adding device /dev/sdb2 id 2
  fs created label SSDRAID1 on /dev/sda3
          nodesize 16384 leafsize 16384 sectorsize 4096 size 117.25GiB
  Btrfs v3.14.2

• Verify:

  # btrfs filesystem show
  Label: 'SSDRAID1'  uuid: 3a69524a-97d1-4255-ab39-9ebf206f3f61
          Total devices 2 FS bytes used 112.00KiB
          devid    1 size 57.62GiB used 2.03GiB path /dev/sda3
          devid    2 size 59.62GiB used 2.01GiB path /dev/sdb2
  
  Btrfs v3.14.2

• Add to /etc/fstab:

  LABEL=btrfsmirror	/mnt/gentoo		btrfs	defaults,noatime	0 0
  LABEL=btrfsmirror	/mnt/gentoo/root	btrfs	defaults,noatime,compress=lzo,autodefrag,subvol=root	0 0

• Mount new btrfs filesystem:

  # mount /mnt/gentoo

• Create BTRFS subvolumes:

  btrfs subvolume create /mnt/gentoo/root
  btrfs subvolume create /mnt/gentoo/root/home
  btrfs subvolume create /mnt/gentoo/root/var

• Verify:

  #  btrfs subvolume list /mnt/gentoo/
  ID 258 gen 9 top level 5 path root
  ID 259 gen 8 top level 258 path root/home
  ID 260 gen 9 top level 258 path root/var
  
  # btrfs fi df /mnt/gentoo
  Data, RAID1: total=1.00GiB, used=512.00KiB
  Data, single: total=8.00MiB, used=0.00
  System, RAID1: total=8.00MiB, used=16.00KiB
  System, single: total=4.00MiB, used=0.00
  Metadata, RAID1: total=1.00GiB, used=160.00KiB
  Metadata, single: total=8.00MiB, used=0.00
  unknown, single: total=16.00MiB, used=0.00

• Check and set date:

  # date
  Thu Dec 18 19:56:19 UTC 2014
  # date [MMDDhhmm[[CC]YY][.ss]]
  
  #or
  ntpdate ntp1.polaire.nl

• Download stage3 tarballs, go to releases/amd64/autobuilds/ on a mirror nearby:

  # cd /mnt/gentoo/root
  # links http://www.gentoo.org/main/en/mirrors.xml
  
  stage3-amd64-20141204.tar.bz2.CONTENTS
  stage3-amd64-20141204.tar.bz2.DIGESTS
  stage3-amd64-20141204.tar.bz2.DIGESTS.asc

• Verify integrity:

  # openssl dgst -r -sha512 stage3-amd64-<release>.tar.bz2

• Verify cryptographic signature:

  # gpg --recv-keys 0xBB572E0E2D182910
  # gpg --verify stage3-amd64-20141204.tar.bz2.DIGESTS.asc 

• Unpack tarball:

  # tar xvjpf stage3-*.tar.bz2

• Edit /mnt/gentoo/root/etc/portage/make.conf:

  # vi /mnt/gentoo/root/etc/portage/make.conf
  CFLAGS="-march=native -O2 -pipe"
  CXXFLAGS="${CFLAGS}"
  MAKEOPTS="-j5"
  
  USE="bindist mmx sse sse2 systemd -consolekit"

• Select mirror:

  # mirrorselect -i -o >> /mnt/gentoo/root/etc/portage/make.conf
  # mirrorselect -i -r -o >> /mnt/gentoo/root/etc/portage/make.conf

• Copy DNS info:

  # cp -L /etc/resolv.conf /mnt/gentoo/root/etc/

• Mount special file systems:

  # mount -t proc proc /mnt/gentoo/root/proc
  # mount --rbind /sys /mnt/gentoo/root/sys
  # mount --rbind /dev /mnt/gentoo/root/dev

• Enter new environment:

  # chroot /mnt/gentoo/root /bin/bash
  # source /etc/profile
  # export PS1="(chroot) $PS1"

• Install a portage snapshot:

  # emerge-webrsync

• Update portage tree to latest version:

  # emerge --sync --quiet

• Select profile if needed:

  # eselect profile list
  # eselect profile set <num>

• Create symlink for SystemD:

  # ln -sf /proc/self/mounts /etc/mtab

• Re emerge in order to compile with systemd :

  # emerge -avDN @world

• Install VIM:

  # emerge --ask vim

• Configure timezone:

  # echo "Europe/Amsterdam" > /etc/timezone

• Reconfigure the sys-libs/timezone-data package:

  # emerge --config sys-libs/timezone-data

• Configure locale:

  # vi /etc/locale.gen
  en_US ISO-8859-1
  en_US.UTF-8 UTF-8
  
  # locale-gen
  # locale -a

• Set system wide locale:

  # eselect locale list
  # eselect locale set <num>

• Reload environment:

  # env-update && source /etc/profile

• Install kernel sources:

  # emerge --ask sys-kernel/gentoo-sources

• Install pci utils:

  # emerge --ask sys-apps/pciutils

• Configure kernel:

  # cd /usr/src/linux
  # make menuconfig
  
  CONFIG_AUTOFS4_FS
  CONFIG_CGROUPS
  CONFIG_FANOTIFY
  
  ##BTRFS
  General setup  --->
    [*] Initial RAM filesystem and RAM disk (initramfs/initrd) support
  File systems  --->
    <*> Btrfs filesystem support
    [*]   Btrfs POSIX Access Control Lists
  
  ##SystemD
  Gentoo Linux --->
          Support for init systems, system and service managers --->
                  [*] systemd
  
  ##devtmpfs
  Device Drivers  --->
      Generic Driver Options  --->
          -*- Maintain a devtmpfs filesystem to mount at /dev
          [*]  Automount devtmpfs at /dev, after the kernel mounted the rootf

• Compile kernel:

  make -j5 && make modules_install
  make install

• Build initramfs:

  # emerge genkernel
  # genkernel --install initramfs
  
  # ls /boot/initramfs*

• Create swap:

  # mkswap /dev/sda2
  Setting up swapspace version 1, size = 2097148 KiB
  no label, UUID=6de68c5a-1c90-4b25-b019-00def47e6c35

• Configure /etc/fstab:

  LABEL=btrfsmirror       /       btrfs   defaults,noatime,compress=lzo,autodefrag,subvol=root    0 0
  UUID="6de68c5a-1c90-4b25-b019-00def47e6c35"     none    swap    sw      0 0

• Configure networking:

  # vi /etc/conf.d/hostname
  
  # vi /etc/conf.d/net
  dns_domain_lo="homenetwork"
  config_enp4s0="dhcp"
  #  emerge --ask --noreplace net-misc/netifrc
  

• Edit /etc/hosts

  127.0.0.1     tux.homenetwork tux localhost

• Set root password:

  passwd

• Edit /etc/rc.conf
• Edit /etc/conf.d/keymaps
• Edit /etc/conf.d/hwclock

• Install mailx:

  # emerge --ask virtual/mailx
  # emerge --config =mail-mta/nullmailer-1.13-r4

• Install logrotate:

  # emerge --ask app-admin/logrotate

• Install syslogger:

  # emerge --ask app-admin/syslog-ng
  # systemctl enable syslog-ng.service

• Install cron:

  # emerge --ask sys-process/cronie
  # systemctl enable cronie.service

• Install file indexing:

  # emerge --ask sys-apps/mlocate

• Install DHCP client:

  # emerge --ask net-misc/dhcpcd

• Install grub2:

  # vi /etc/portage/package.use
  sys-boot/grub:2 device-mapper
  
  # emerge --ask sys-boot/grub
  
  # vi /etc/default/grub
  # Append parameters to the linux kernel command line
  GRUB_CMDLINE_LINUX="rootfstype=btrfs rootflags=device=/dev/sda3,device=/dev/sdb2,subvol=root init=/usr/lib/systemd/systemd"
  

• Install grub2 on disks:

  # grub2-install /dev/sda
  # grub2-install /dev/sdb

• Generate config:

  # grub2-mkconfig -o /boot/grub/grub.cfg

• Exit chroot:

  exit

• Umount:

  umount -l /mnt/gentoo/dev{/shm,/pts,}
  umount /mnt/gentoo{/boot,/sys,/proc,}
  reboot