Synology

Storage Pools

Think of a storage pools as a group of your HDDs that you decide to group

Storage pools are mostly about RAID levels. If you want one RAID for all disc - use one pool for all of them. But maybe you want to have large HDD for storage and fast SSD for docker? Obviously you don't want to put HDD and SSD in one RAID. So, you'll have two storage pools.

you cannot reduce an existing Storage Pool's number of drives or replace its drives with smaller capacity ones, since data are distributed across the drives in most RAID types

if you must, follow the guide to do so

Volumes

A volume is a collection of HDDs (or even just one)

Volumes provide the basic storage space on your Synology NAS. All of your stuff—such as shared folders, documents, and package data—is stored on volumes. Therefore, before you start storing anything on your Synology NAS, you will need to create at least one volume.

Think of a volume as a Partition, if you think of the RAID group as one HDD.

Your volume is assigned to a Storage Pool and does not know what is the underlying hardware structure of that pool.

mostly about filesystem: ext4 vs btrfs.

Unless you have specific reason and you know what you're doing, - just use btrfs and do one volume per storage pool.

You may want to create multiple volumes if you previously created multiple pools with the same or different type of RAID and/or disk numbers

Example usage

volume 1 is 6 bays and holds my data, movies, personal photos etc
volume 2 is a single drive that records surveillance and therefore is very heavy use. I don't want all my disks working that hard. I figure it would be a slim coincidence for it to go when I do need to review its data.
volume 3 is a single SSD for my dockers including plex config for speed purposes. backup up daily, so no big deal if I lose a day.

Folders inside the Volume.