Extend save partition

Hello guys,

I would like to extend a save partition in my ubuntu, I would like to add 20 GB from home partition using command line.

# df -h
Filesystem      Size  Used Avail Use% Mounted on
/dev/root        29G   25G  3.2G  89% /
devtmpfs         16G     0   16G   0% /dev
tmpfs            16G  8.0K   16G   1% /dev/shm
tmpfs            16G  3.3M   16G   1% /run
tmpfs           5.0M     0  5.0M   0% /run/lock
tmpfs            16G     0   16G   0% /sys/fs/cgroup
/dev/md5         29G   29G     0 100% /save
/dev/md3        2.7T  2.5T   49G  99% /home
tmpfs           3.2G     0  3.2G   0% /run/user/1000

System information:

# lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 18.04.4 LTS
Release:        18.04
Codename:       bionic

Thanks in advance

More details, please. Guessing by their device names, we're dealing with a "Linux Software RAID" implemented by the Multiple Device driver. We at least need the RAID level, i.e. "The manner in which the devices are arranged into the array", and the layout on disk.

I'm not sure about layers information:

Datacenter
RBX2 - Rack: 21B13 - Server ID: 538852
OS
Xubuntu Desktop 14.04 "Trusty Tahr" (XFCE + x2go) (64bits)
Boot
OVH kernel (includes up-to-date intel microcodes)
Server OP-SAT-1-32 - Opteron 4334 - 32GB - SoftRaid 2x3To