How to use boot pool space for VMs in TrueNAS scale

TrueNAS General
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Hello,

To whom it might concern, I read a post a guy asking how to use the boot-pool space here
Solutions were to reinstall manually found on a reddit post.

Maybe it’s just plain stupid, but I had to create a KVM VM on TrueNAS, and wanted it to reside on boot-pool.

Solution is crazy simple:

  • Create a ZVOL via zfs create -V 100G boot-pool/myvm
  • Use said zvol in VM creation via ‘use existing disk’

Sorry if this is already well known knowledge, but I thought it might be useful.

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Except your zvol will be erased at the next system upgrade…

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This is very interesting but raises some questions:

Will this persist with truenas version upgrades?

Are you testing this on a non prod system ?

What happens if you need to go to a previous snapshot of the boot pool, won’t this also revert your vm?

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Fair enough, that’s the reason I posted here, in order to know whether this is an acceptable practice or not.

I do understand that TrueNAS is an enterprise grade solution, which doesn’t need soho user tinkering. I used to own a couple of TrueNAS X20 HA units a couple of years ago, which were rock stable (except of some link flapping, but that’s another story).

In my current usecase, I have 2x1TB NVME boot drives + 8x20TB enterprise HDDs on a supermicro 3U server.

In order to have my backup VM reside on the TrueNAS unit and not waste perfect NVME drives, I could imagine going the following route:

  • Buy 2x small SSD read intensive drives and reinstall TrueNAS on it
  • Partition the NVME drives into 2 partitions
  • Use 1 partition for “quick” VM storage
  • Use 1 partition as ZIL (the drives are write intensive)

Would this be an accpetable practice ?

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It’s possible the zvol won’t be mounted when you next update. Or it might.

You’d have to test.

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The whole point about using a full drive for boot is to make it disposable: Save the configuration file; when needed, reinstall anew and load the saved configuration.
Mirrorring the boot drive is essentially pointless for home use.

But buying one (or two, if you really want) cheap and small SSD is absolutely the way to go.

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Again, fair point. But 40€ read intensive 120gb ssd x2 isn’t worth not mirroring :wink:

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IMHO true if in case of need the Nas must go back online fast (reboot → change boot prio → save and reboot)… In other case you waste a bit a disk (reinstall → upload config have reasonable time )

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This sounds like a validation escape. Boot pools shouldn’t be used in this way

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