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====== A "perfect" btrfs server ======


This is nearly the title of a fine [[https://seravo.fi/2016/perfect-btrfs-setup-for-a-server|article]] (signed by Mr Technology...) and my notes of its implementation.

It is tested only on legacy boots, and is known not to work as is on some UEFI boots.

The interest of btrfs is big, and many good articles explain it, but I have not found good articles on its implementation on debian. The server is based on a debian with 2 RAID1 2T disks.

===== Install basic debian =====

Let us start to install the system from debian-9.1.0-amd64-netinst.iso (on a flash USB key in this case). I skip here standard install procedures but,on the partition menu, create a main btrfs partition on the whole first disk, add the boot flag, mounted on /. On the second disk create a partition as on the 1rst disk but declare it of type "not in use",but with the boot flag. Do not declare any other partition. Finish the installation normally.

As is, my system refused to boot, but with the USB key mounted, the system boots...
And I had to :
<code>
grub-install /dev/sdX1
apt install --reinstall grub-pc
</code>
and then it boots.

We have now a basic server with btrfs file system.


===== Build the RAID1 =====

We note /dev/sda and /dev/sdb the two disks, but it may differ on other systems.

If not soon done, add the boot flag //now// with fdisk to the second disk. Then add the 2nd disk to / and build the RAID:
<code>
apt update
apt install btrfs-tools
btrfs device add /dev/sdb1 /
btrfs balance start -v -mconvert=raid1 -dconvert=raid1 /
</code>
You can use btrfs display commands to see the sitation all along :
<code>
btrfs fi show
sudo btrfs fi usage /
</code>

===== Various inits  =====

I suggest to modify les logs dans /etc/systemd/journald.conf :
<code>
Storage=persistent
</code>
See : https://guillaume.fenollar.fr/blog/journald-tutoriel-journald-journalctl/

==== Add zram based swap ====

Ubuntu policy is to assign half of the memory to swap and divide it by the the number of CPU hearts.
<code>
apt install zram-tools
</code>
You should  modify ALLOCATION to 33-50% or total RAM in /etc/default/zramswap


===== Install lxd =====

The interest of "containers" is great to isolate problems. I have choosen [[https://linuxcontainers.org/lxd/|LXD]]. To say it simply, LXD is magic... Thanks to the developper team.

==== Prepare the bridge ====

Create a simple bridge :
<code>
apt install bridge-utils
</code>
In /etc/network interfaces, //here// based on enp5s0 (not //wan//) interface :

<code>
# The loopback network interface
auto lo
iface lo inet loopback



# The primary network interface
auto enps5s0
iface enp5s0 inet manual


auto br0
iface br0 inet static
        address 192.168.163.1
        netmask 255.255.255.0
        gateway 192.168.163.254
        network 192.168.163.0
        broadcast 192.168.163.255
        bridge_ports enp5s0
        bridge_stp on
        bridge_maxwait 0
        
iface enp5s0 inet6 auto        
</code>

==== Install lxd from snap ====


<code>
apt install snapd
snap install lxd
</code>
Logout, then log in again, then init lxd.

==== Initialize LXD ====

Default values are usually good (btrfs...), but //do not declare any network// but add br0 "manually" after, then add your user to lxd group  :

<code>
lxd init
[...]
lxc network attach-profile br0 default eth0
adduser myuser lxd
</code>

Now myuser can manipulate containers :
<code>
lxc launch images:debian/stretch debian
lxc config device  override debian eth0 hwaddr=02:1E:62:00:00:36 (recommended)
lxc config set  debian  volatile.eth0.hwaddr  00:1e:62:00:00:43 (not recommended)

lxc start debian
lxc exec  debian bash
...
</code>
It is possible to choose to work as root in the containers as they are isolated from the host.

====  Containers LXD ====
=== Backup ===
<code>

lxc export pgsql /media/lxd_containers/pgsql2020_01_12.tar.gz
</code>
After import, the container is on stopped state :
<code>
lxc import  /media/lxd_containers/pgsql2020_01_12.tar.gz
</code>

=== Use simple mail in server or containers ===
== nullmailler ==
Bien
== msmtp ==

<code>
apt install msmtp msmtp-mta
</code>

Et /etc/msmtprc :

<code>
account default
host 192.168.13.36
auto_from off
from container_name@couderc.eu
syslog LOG_MAIL
</code>

== Data access ==
<code>
/var/snap/lxd/common/mntns/var/snap/lxd/common/lxd/storage-pools/default/containers/
</code>
===== Maintenance =====

In case of failure, prevent the problem by having a 3rd empty disk ready...

To replace :

<code>
btrfs fi show
btrfs replace start -rf /dev/sdb2 /dev/sda2 /
</code>