Some Drive questions

[intavg]

Getting ready to build my first TrueNAS system using TrueNAS Scale, and am trying to figure out the drives that I should purchase for this, and have a few questions on the drive layout:

1- For the OS drive, is there any reason not to use an NVME drive if it is supported by the hard drive? I see a lot of references to SSDs specifically, but not much about using NVME. Is it not supported?
2 - If NVME is ok to use, and if I get a motherboard that supports multiple NVME drives, would it be worthwhile to install two, with one being the live OS and the other being a backup of the OS? I've seen references to this approach being used with USB OS drives, not sure if that still applies with SSD / NVME?
3 - For the data pools, I saw in the documentation for Core that a hard drive can be installed and designated as a hot standby. Is that the case with Scale as well?
4 - Can I set up multiple data pools where most have multiple drives in RAID arrays, and one pool consists of a single drive? This pool is for test builds, where if the data is lost its not a big deal.

What I am thinking of is a system with eight SATA drives, two NVME drives, as follows:
M2-1 - OS
M2-2 - Backup OS
HD-1 - Pool 1
HD-2 - Pool 1
HD-3 - Pool 1
HD-4 - Pool 2
HD-5 - Pool 2
HD-6 - Pool 2
HD-7 - Pool 3
HD-8 - Hot Spare

 

[NugentS]

1. NVMe is fine to boot from. Just remember that a boot drive does not require significant performance so you are wasting its potential. Also 16GB is about minimum sensible. 32 GB is probably better.
2. Almost not worth it. As long as you keep a copy of your config file somewhere safe (not on the NAS) then you can easily rebuild. You can do this but most machines won't boot from the second drive (without reconfiguring things). Rebuilding the NAS from ISO is very very simple
3. Yes. Note its a hot standby in a single pool, not across multiple pools
4. You can have as many pools as you like (subject to the limits of the number of disks)

Make sure you don't buy SMR drives

 

[Arwen]

Hot spares can be shared between pools, until it becomes in use for 1 pool.

Some people here don't suggest hot spares, because of easy availability to manually install a replacement drive. (Using a cold spare, aka a disk on the shelf, pre-burned in.) However, hot spares are useful for people who might be gone alot, or their NAS is in a remote location.

Further, except in the case of multiple pools, or extreme performance reasons, an extra online disk could be additional parity for a pool.

 

[NugentS]

Am I wrong again?
I had no idea that you could share a hot spare between pools

 

[ChrisRJ]

Getting ready to build my first TrueNAS system [..]

Congratulations!

Please be aware that a NAS, like any server, has different requirements w.r.t. the hardware than a typical desktop machine. I am mentioning this because these days many people come to TrueNAS because of shady YouTube videos that convey how easy it is to build a NAS with gamer gear or old stuff that is laying around. If you want to entrust valuable data (like photos), this may be dangerous.

Here are a few things you should have a look at (plus the "Recommended readings" in my signature):

Welcome to TrueNAS SCALE - Beginners Intro

Since mid 2021 we have had many new users of TrueNAS wanting to try SCALE. Here are some things that are helpful for new TrueNAS SCALE users to know; SCALE is a specialized & targeted OS based on a Linux distro. However, SCALE is NOT a Linux...

www.truenas.com

Hardware Recommendations Guide

This is the latest edition of the FreeNAS Community hardware recommendations guide. The current major version is R2, dated January 2021, with the last minor update on 2021-01-24. The format has moved away from the forum post form factor, to...

www.truenas.com

Introduction to ZFS

This is a short introduction to ZFS. It is really only intended to convey the bare minimum knowledge needed to start diving into ZFS and is in no way meant to cut Michael W. Lucas' and Allan Jude's book income. It is a bit of a spiritual...

www.truenas.com

 

[Arwen]

Am I wrong again?
I had no idea that you could share a hot spare between pools

Yes, you are wrong, this once . I thought I was wrong too, once, but I was wrong .

Here is the info from the zpoolconcepts manual page for spares:

Spares can be shared across multiple pools, and can be added with the zpool add command and removed with the
zpool remove command. Once a spare replacement is initiated, a new spare vdev is created within the config-
uration that will remain there until the original device is replaced. At this point, the hot spare becomes
available again if another device fails.

If a pool has a shared spare that is currently being used, the pool can not be exported since other pools
may use this shared spare, which may lead to potential data corruption.

Shared spares add some risk. If the pools are imported on different hosts, and both pools suffer a device
failure at the same time, both could attempt to use the spare at the same time. This may not be detected,
resulting in data corruption.