I recently started setting up multiple TrueNas Servers, all with mirrored OS discs.
I noticed that on every machine the System Dataset Pool was set to other Datasets like my Data Mirror. I went ahead and set it to the “boot-pool”
My NASes only host file via SMB nothing heavy load. Why does the OS move this to my data partitions and is there any downside of having this on the boot-pool?
By default the system dataset gets placed on the first Data Pool that gets created.
If you’re using ssds for the boot-pool (which you should) then there’s no downside to put in on there.
I guess it’s a relic from the time when you could use usb thumb drives for the boot disks and the constant writing of the system dataset would wear it out faster.
Thanks for the Info. All my OS drives are flash-based and redundant, so I’m fine with having it on the boot-pool. Just needed this kind of confirmation because I’m new to TrueNas
Again thanks m8
You do lose the system dataset if you ever need to reinstall though. If it’s on some other pool you can just swap boot disks, restore the config and everything is as it was before.
Iirc the system dataset doesn’t store anything critical, just reporting, logs, caches and such stuff but you still lose it in that case. I now have redundant boot disks as well but before that I had to switch boot disks a few times and it never took me more than 20min because it was just reinstall, restore config, done.
It’s a requirement on the enterprise side of our product related to high availability.
Ah ok, good to know 
Do enterprises also often have it running on the boot-pool? I would assume yes..
I doubt it, since truenas HA works with 2 controller units with different boot-pools. If there’s a need to switch the contoller unit because of a hardware failure you’d also loose the system dataset, if its on the boot pool of unit 1. If it’s on a storage pool, the second controller can use it, at least thats how i imagine it works.
No. There is generally not a reason to ever put it on the boot pool.
The .system dataset will also contain things like the configuration DB, directory services info, etc that you really want to be common and sharable across both halves of an HA system so that a failover Just Works™ and allows you to continue serving data without interruption.
I’d also recommend against it even as a home user, but with mirrored high-endurance boot devices and a pool made entirely of HDDs one might consider it - with the understanding that if you lose both boot devices at once, you won’t be able to fish out the auto-config backups and get back up and running as quickly on a new install.
