Welcome to TrueNAS!
To start I suggest you reading the following resources in order to gain a basic understanding about how ZFS works.
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...
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1) An HBA is a Host Bus Adapter. This is a controller that allows SAS and SATA devices to be attached to, and communicate directly with, a server. RAID controllers typically aggregate several disks into a Virtual Disk abstraction of some sort...
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This resource was originally created by user: @Davvo on the TrueNAS Community Forums Archive. https://www.truenas.com/community/resources/zfs-storage-pool-layout.201/download [1] This amazing document, created by iXsystems in February 2022 as a “White Paper”, cleanly explains how to qualify...
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Then I suggest you to look at the Hardware Reccomendation 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...
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Now, it is my opinion that given your needs it will be hard to build a system around low power consumption since:
A) given your listed uses, it will be hard to reach deep C states;
B) given the amount of space you listed (40TB) you will have quite a few drives.
Now, I would really like to specify what do you mean by that
HDDs: 40TB
. Please specify how many HDDs you have, their model and their sizes.
You will need at least a pair of SSDs for your Apps and VM pool alongside your storage pool.
Without knowing how many HDDs you have it will be difficult to suggest you a motherboard since you want to use its sata ports and not use an HBA (since afaik they don't like to go to deep C states).