synology "disk groups" vs "volumes" clarification

Question

Synology has introduced some interesting terminology with their products that is confusing (to someone used to traditional storage terminology).

It appears that "volumes" on Synology is equivalent to RAID volumes. But then:

1. What are "disk groups"? (Is this JBOD)?
2. What is SHR? (Another synology specifig term)?

Solution

In Synology terminology a disk group is simply a RAID array that can then be split it up into several volumes.

So if you have 4 disks, you can create one single disk group (RAID array) and create two volumes from it. Or you could create 2 disk groups, and create one volume on each.

The difference / advantages being that the single array will have more space, while the separate arrays will have better redundancy.
There is a nice write-up on the synology forums about this

SHR is a separate concept, and is based on the Linux Raid Management system.
It's a design that allows for the usage of otherwise unused space on larger disks added to an array limited by a smaller disk.

Full disclosure, I use synology at home but have never been involved with our NAS at work

Comments

[TSG]

Is there any impact in terms of ability to grow the array? For example, I have 1 raid0 array (volume) spread over 2 disks, and no disk groups. If I added a third disks, can I add it to my volume? If I had create a single disk group first, would I then be able to add it to my 1 volume?

[Reaces]

@GenerationDSystems Not really no. You will have to add the disk to your disk group, and then choose a volume to expand. Keep in mind though that expanding an SHR is very slow.