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Install TrueNAS on a partition rather the full disk

So i bought my 2nd Ugreen DXP2800 and could finally do some more testing 😀 and perform a writeup.

You can find the updated version in my Github GIST How to install TrueNAS SCALE 25.10 on a partition instead of the full disk + mirror boot and data partition at a later stage

Because the TrueNAS installer doesn’t support usage of anything less than the full drive, a lot of space will be wastetd installing it to a large SSD/NVMe. TrueNas OS will only use a few GB for it’s system files so installing to a 16GB partition is sufficient.

NOTE: As of this writing, TrueNAS Scale recommends a 20GB boot drive. For more details, visit https://www.truenas.com/docs/scale/gettingstarted/install/installingscale/

This guide covers for TrueNas Scale 24.04 to 25.10

You will have to modify the installer script before starting the installation process.

  1. Boot TrueNAS Scale installer from USB/ISO
  2. Select shell in the first menu (instead of installing)
  3. While in the shell, find and open the installer and edit using vi

For TrueNasScale before 24.10 – https://github.com/truenas/truenas-installer/blob/release/24.04.2.5/usr/sbin/truenas-install#L460

vi /usr/sbin/truenas-install

For TrueNasScale 24.10+ – https://github.com/truenas/truenas-installer/blob/76a188e9048f26bca1a88f5d46a552742b3db286/truenas_installer/install.py#L81

vi /usr/lib/python3/dist-packages/truenas_installer/install.py
  1. in vi you can use “set number” to easily see on what line of code you are
  2. make the changes on line 81 as follows: await run(["sgdisk", "-n3:0:+16GiB", "-t3:BF01", disk.device])
  3. exit vi and type exit to return from the shell
  4. Select Install/Upgrade from the Console Setup menu (without rebooting, first) and install to NVMe drive.
  5. Remove the USB and reboot.

Next we re-partition the nvme. You can perform this next setp on console or enable ssh via TrueNas Gui

  1. Login to the linux shell.
  2. Verify the created partition and their alignment
truenas_admin@truenas[~]$ sudo fdisk -l /dev/nvme0n1
Disk /dev/nvme0n1: 931.51 GiB, 1000204886016 bytes, 1953525168 sectors
Disk model: CT1000P3PSSD8
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: 67X88FDC-3A4E-43FC-BA2F-AD279703FBFF

Device           Start      End  Sectors  Size Type
/dev/nvme0n1p1    4096     6143     2048    1M BIOS boot
/dev/nvme0n1p2    6144  1054719  1048576  512M EFI System
/dev/nvme0n1p3 1054720 34609151 33554432   16G Solaris /usr & Apple ZFS


truenas_admin@truenas[~]$ for p in 1 2 3; do sudo parted /dev/nvme0n1 align-check optimal $p; done
1 aligned
2 aligned
3 aligned
  1. create a partition allocating the rest of the disk.
(parted) name 3 boot-pool
(parted) mkpart ssd-pool 17304576kiB 100%
(parted) print
Model: CT1000P3PSSD8 (nvme)
Disk /dev/nvme0n1: 976762584kiB
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Disk Flags:

Number  Start        End           Size          File system  Name       Flags
 1      2048kiB      3072kiB       1024kiB                               bios_grub, legacy_boot
 2      3072kiB      527360kiB     524288kiB     fat32                   boot, esp
 3      527360kiB    17304576kiB   16777216kiB   zfs          boot-pool
 4      17304576kiB  976761856kiB  959457280kiB               ssd-pool

truenas_admin@truenas[~]$ for p in 1 2 3 4; do sudo parted /dev/nvme0n1 align-check optimal $p; done
1 aligned
2 aligned
3 aligned
4 aligned
  1. setup the zpool for the UI to pick it up

sudo zpool create ssd-pool /dev/nvme0n1p4 sudo zpool export ssd-pool

use the TrueNas Gui -> Storage Dashboard -> Import Pool