Finally, I found a solution to the issue:
https://www.truenas.com/community/threads/multiple-ada0-partitions-on-xen-pv-w-passthrough.16574/

set via GUI tunables interface:

hint.ada.0.at="scbus100".

Works perfectly!

root@truenas[~]# geom disk list
Geom name: ada0
Providers:
1. Name: ada0
   Mediasize: 53687091200 (50G)
   Sectorsize: 512
   Mode: r1w1e2
   descr: (null)
   ident: (null)
   rotationrate: unknown
   fwsectors: 0
   fwheads: 0

Geom name: cd0
Providers:
1. Name: cd0
   Mediasize: 0 (0B)
   Sectorsize: 2048
   Mode: r0w0e0
   descr: QEMU QEMU DVD-ROM
   ident: (null)
   rotationrate: unknown
   fwsectors: 0
   fwheads: 0

Geom name: ada1
Providers:
1. Name: ada1
   Mediasize: 4000787030016 (3.6T)
   Sectorsize: 512
   Stripesize: 4096
   Stripeoffset: 0
   Mode: r0w0e0
   descr: ST4000LM024-2U817V
   lunid: 5000c500d5b4af0c
   ident: WCK7ABLM
   rotationrate: 5400
   fwsectors: 63
   fwheads: 16

Geom name: ada2
Providers:
1. Name: ada2
   Mediasize: 4000787030016 (3.6T)
   Sectorsize: 512
   Stripesize: 4096
   Stripeoffset: 0
   Mode: r0w0e0
   descr: ST4000LM024-2U817V
   lunid: 5000c500d5b3d1cb
   ident: WCK7ADS1
   rotationrate: 5400
   fwsectors: 63
   fwheads: 16

Sata controller passthrough. VM no bootable device