What filesystem to use inside VM?

TrueNAS General
1

Hello,

when deploying a Virtual Machine on TrueNAS SCALE it gets a Zvol that is handled as block device inside the VM. What are the preferred file systems to use inside the VMs on such Zvol block devices?

I think using ZFS inside the VMs makes no sense, as the Zvol is already protected by ZFS and using “ZFS inside ZFS” sound a bit faulty to me.

Should I simply use something like ext4 inside the VMs or do you have any recommendations?

Thanks a lot in advance,

Thomas

2

Yes, whatever non-CoW file system the guest OS uses—because ZFS-on-ZFS or generally CoW-on-CoW is an inefficient waste.

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3

Do a bit of reading on suitable ZVOL block sizes for your VM’s workload - there is a fair bit of info on that out there e.g.

Also see the note about sparse zvols and TRIM.

4

I like to use LLVM, predominately because it’s the Ubuntu default and then I can use my guide to resizing the ZVol whenever I want :wink:

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5

To take a contrary position, I generally avoid LVM and any other kind of volume manager for VMs, preferring to let the host deal with that sort of thing. Bare ext4, and if I need to resize it, it’s:

  • Increase virtual disk size in the hypervisor
  • In the VM, parted /dev/sda resizepart 1 100%
  • In the VM, resize2fs /dev/sda1

Easy-peasy.

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6

Agree and I will go one step further

Just use RAW files and forget the complications of a ZVOL.

Been using them since I moved 100% of my VMs (from ESXi) and few Apps (from TrueNAS Core) to SCALE, more than 2 years ago?

Yes, the darn GUI does not let you create the raw files, but once you create or convert the files, you can select them in the GUI.

7

What exactly do you mean with raw files?

8

What “complications” are those? And what benefits do you see to using RAW files instead?

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9

It’s not a complication, if you know, but how does a newbie copy a zvol?

Regardless, I find copying/moving simple files always beats figuring out zvol names and zfs commands.

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If I was a newbie, personally I’d research use the well documented features that are ZFS bread-and-butter like snapshots and clones, which can be created via the UI, rather than wasteful file copying.

11

Why does a newbie (or anyone else) need to?

That’s why the GUI is there, so you don’t need to.

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