Running a NAS on Debian is a great idea if you don’t mind being responsible for all of the details that TrueNAS abstracts away. One thing I’d consider in your shoes is to use Proxmox VE rather than vanilla Debian. I say this because PVE uses a kernel with ZFS built in, so there’s no fiddling with DKMS to get it to work; it just treats it as a first-class file system (including on root). Having said that, either is a perfectly good choice.
If you want a UI, I’d heartily recommend Cockpit, which is included in the repos (just apt install cockpit). If you go the PVE way, you’ve got a couple options. You could either virtualize your existing TrueNAS, passing through the disks or (and this is my preference) let the host handle all the ZFS stuff and create an LXC container that just deals with filesharing. You’d bindmount a directory from the host that could be shared out via SMB and this is where I’d use Cockpit to manage the shares.
The PVE route makes adding VMs and containers pretty quick. I haven’t run into any issues passing through a GPU to either a VM or LXC, which can then be used inside a docker container.
In answer to the common pitfalls question, I think the biggest thing I see is that it’s important to document exactly what TrueNAS is doing for you. Did you encrypt the ZFS pool? Make sure you have the keys to unlock it and arrange for your next OS to do so gracefully. Are you managing snapshots and replication in TrueNAS? Document and adapt that. Something like sanoid/syncoid can manage this on a Debian system. How about monitoring? Don’t forget to set up notifications for disk failures. Any other services you’re using? NFS, iSCSI, cronjobs? Take care notes of everything because that’s the stuff that’ll be easy to miss if you jump straight to overwriting your old boot disk.
Here’s one more opinion for you.
Running a NAS on Debian is a great idea if you don’t mind being responsible for all of the details that TrueNAS abstracts away. One thing I’d consider in your shoes is to use Proxmox VE rather than vanilla Debian. I say this because PVE uses a kernel with ZFS built in, so there’s no fiddling with DKMS to get it to work; it just treats it as a first-class file system (including on root). Having said that, either is a perfectly good choice.
If you want a UI, I’d heartily recommend Cockpit, which is included in the repos (just
apt install cockpit). If you go the PVE way, you’ve got a couple options. You could either virtualize your existing TrueNAS, passing through the disks or (and this is my preference) let the host handle all the ZFS stuff and create an LXC container that just deals with filesharing. You’d bindmount a directory from the host that could be shared out via SMB and this is where I’d use Cockpit to manage the shares.The PVE route makes adding VMs and containers pretty quick. I haven’t run into any issues passing through a GPU to either a VM or LXC, which can then be used inside a docker container.
In answer to the common pitfalls question, I think the biggest thing I see is that it’s important to document exactly what TrueNAS is doing for you. Did you encrypt the ZFS pool? Make sure you have the keys to unlock it and arrange for your next OS to do so gracefully. Are you managing snapshots and replication in TrueNAS? Document and adapt that. Something like sanoid/syncoid can manage this on a Debian system. How about monitoring? Don’t forget to set up notifications for disk failures. Any other services you’re using? NFS, iSCSI, cronjobs? Take care notes of everything because that’s the stuff that’ll be easy to miss if you jump straight to overwriting your old boot disk.