How do i use my boot mirror pool as storage for vm's and such?

TrueNAS General
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1

im using 2 15k boot drives 300gb and only 3gb is used, its a fresh installation so i made mostly zero changes.
if that matters they are Seagate savvio 15k.3 inside a dell poweredge R730xd

2

You can’t.[1] The boot drive is the boot drive, period. That’s the way TrueNAS (and FreeNAS before it) has always been, and almost certainly always may be.

  1. In any supported way. Yes, it’s possible to hack it in, and if you search the forum, you’ll find some descriptions of how to do it, but you’re very much on your own in that regard. ↩︎

3

cant you just make a small 40gb partition on the disk for truenas and just make the rest for storage/whatever

4

Can you? Sure. But if you have to ask how, you shouldn’t be doing it.

The design of Free/TrueNAS has always been to have a dedicated boot device. That’s highly unlikely (IMO, naturally) to ever change. Yes, you can hack around it, but you do so at your own risk.

5

A lazy option that draws within the lines of what is supported would be to not have mirrored boot drives. Use 1 drive for boot, use 1 drive for ‘vms & such’.

Unless you’re chasing five 9’s, it is really pointless from any perspective that allows 15 minutes downtime to shut down, swap a boot drive, reinstall truenas, & import a config. Recovering from a failed boot drive (if you have a backup of your config; you always should) is very painless.

…this is coming from someone with mirrored boot drives; I’ve only used it once to allow me to hot swap a boot drive without shutting down the system. It felt cool - but I cannot stress enough that it is fairly pointless.

Edit: there is also the problem of mirrored boot drive roulette. Your bios doesn’t care that you have mirrored boot drives, it wants to boot from drive A, not drive B. If drive A is failed, but not bad enough that it is no longer detected, there is a chance that your bios will continue to try (and fail) to boot from drive A!

This creates an interesting problem where your server is now failing to boot even though you have boot redundancy. Especially annoying if you are away from home.

There was a long post about this problem & some interesting workarounds with THREE drives back on the old forums

6

i see. that seems fine then. i wanted truenas to feel like using a hardware raid controller where i can hotswap drives if i ever need to (which i would, i have 1 drive with over a petabyte reads)

edited reply: i doubt it would be hard to just manually select the boot device in the bios

7

I don’t blame you, I had the same idea; it was very fun the 1 time I did it. It really is pretty useless in a home environment though.

You’re right - for us it isn’t. But what if you’re not on site & won’t be for an extended period. Ever tried to walk a normie through boot selection on bios? Or worse to physically disconnect the half failed boot drive so system can operate normally?

8

iirc dell servers should clearly detect a hard disk failure and should show you LED’s of which is the bad disk, plus if you installing truenas you should have some basic knowledge on hand already. imo its fine to do also a single boot drive with a brand new ssd, it would last long enough for whatever you need to do + backups.

9

For best results you’d want your VMs to be on a SSD anyway.
15k drives are just LOUD rust.

10

yes and no. im using 2.5 15k, which are quieter, and my dell’s fans drown out any those these things make. only downside is power usage but the upside is they are dirt cheap on ebay vs buying a basic ssd in 2026

11

While unsupported and unrecommended, I had been using this method ever since I responded to that thread: HOWTO: TrueNAS Scale: from 32gb USB to booting from mirrored larger enterprise SSD's, create add'l partition/data pool from remaining free space | TrueNAS Community

And my experience was nice, simpleš, and fast.

This setup has served me really well on a home-scale installation of the more “hack on it” usecase

1 - that will depend on your knowledge a lot. It felt simple to me because it was simpler than making something that’d serve the same needs out of a “regular” Linux box, or, god forbid, windows. I was not even close to considering BSDs or anything else more obscure and/or proprietary (nor am for these).

That being said, I still enable dev mode, have extra scripts and binaries running on the machine, and mess with things like acme.sh with custom CA or one-time things I’d rather not create yet another container for, i.e. badblocks for testing a random drive for someone else.

I also run an extra-sized swap on the same drive because putting it into 2gb partitions onto spinning rust and then having the system barely respond even to keyboard inputs, during a scrub and heavy memory use, let alone over network, is frankly ridiculous. The responses at the time were along the “just get more ram lmao, you don’t have 128gb? How dare you?” lines.

All this is to say: know the risks, don’t expect support, and be willing to waste time, break things, and learn from your mistakes if you’re going this route.

I have made a few backups of the whole disk per-partition via Clonezilla, mostly when upgrading TrueNAS, and am planning to replicate or move “apps” somewhere else now that I have some more available drives (will probably move system to a mirror of sata 60gb drives I received recently instead. Still better than USBs.)