DSM 7.1 Files stored on a pool vs volume

[synn]

I have 3 16TB HDDs in my DS920+ newly setup with a SHR-1 pool and a single volume plus a few basic packages installed. It shows the storage pool as 29.1 TB and the volume size as 27.9 TB (a 1.2 TB difference in size). On the volume it shows about 800 MB as used although I haven't put any of my own data yet.

1. What exactly is stored in the 1.2 TB outside the volume? Will this grow as I fill my volume with data, install apps? What about if I added another 16 TB HDD - will the difference in pool and volume sizes increase?
2. Similarly, what is in the 800 MB? Is it where the OS (DSM) and the packages are installed? If so I assume that OS/package updates can cause this to increase right?
3. Is there a way I can browse ALL the files on the volume (including the os/package files) and not just the shared folders I've created on my NAS which is what File Station seems to show me?
4. I came accross the term 'LUN' it seems related somehow but I couldn't find a good explanation online. Can somebody please explain in a simple way?

 

[Phone Guy]

Ok, I'll take a shot at these too... Again, I am no expert but I will try to answer the ones I think I can to the best of my limited ability... I am sure the experts will chime in too.

1. There is overhead with every package you install, that is normal. Any additional drives will of course increase your volume/pool sizes.
2. I assume again, that is overhead from the DSM and package installation, and yes you can expect that to increase with usage.
3. You could SSH in and get Root privileges and see the entire directory structure *NOT RECOMMENDED!*

 

[synn]

Yes I know that the OS and packages installed will take up disk space - the question was where that space is...outside the volume in the 1.2 TB gap or on the volume in the 800 GB.

I see - can I open a terminal in the web GUI of DSM? So I don't have to ssh in?

 

[Phone Guy]

Not that I am aware of, you would have to enable SSH inside DSM and actually SSH in with your credentials and then get root (in linux) and then you can browse the drives. AFAIK you can not directly access the terminal/ssh cli from the DSM instance/web portal. If this exists, I am not aware of it.

As to the rest of the space used, I dont know. But I've learned synology apps have hidden data not necessarily accessible to the user thru the web gui (file station), like Active backup for business (as I recall), among other apps. Plus, if I remember right, each drive has a portion reserved for the OS (I think I read that somewhere), but in the grand scheme its not enough to loose sleep over. Of course YMMV.

 

[EAZ1964]

Apart from the system partition, that will not grow, and does not take further space than initially partitioned.
BTRFS has around 3% overhead used for the file system.

It makes no sense at all to look in the system partition, you cannot change anything (and should not). Do not waste time worrying about this. It is not windows where you loose 80GB from your 256GB disk for the system and apps alone.

 

[pbondurant]

Yes I know that the OS and packages installed will take up disk space - the question was where that space is...outside the volume in the 1.2 TB gap or on the volume in the 800 GB.

I see - can I open a terminal in the web GUI of DSM? So I don't have to ssh in?

The size of a Pool is the amount of raw disk space. A Volume is this space after being formatted with a file system (likely BTRFS) and is smaller as all filesystems have an overhead (they have to store metadata and their own structures like journals etc). BTRFS also reserves a small percentage of space (up to 5% iirc) to avoid crashing when the disk is very full.

The OS and apps are in a hidden system partition that is copied to all disks in the array - this is your 800MB. As /uEAZ1964 says above, you don't ordinarily need to concern yourself with this system partition. It's much like asking 'where are the system OS files stored on my iPhone?' If you really want to see them, you can do so via SSH.

 

[Rusty]

apps are in a hidden system partition

Most Package Center apps are on the actual volume1 (or whatever number you have), and the OS is on a non-accessible user partition.

I came accross the term 'LUN' it seems related somehow but I couldn't find a good explanation online. Can somebody please explain in a simple way?

Guessing you are talking about iSCSI LUN? It is a type of "logical partition" that is a part of your existing volume or poll depending how you configure it, that will be accessed using an iSCSI initiator from a compatible client side.

That can be a macos, linux, windows machine/server, it can be a hypervisor. The point is that the client side can connect that LUN over network to itself, format it, and then present it to the OS as a "local" hard drive.

It is useful for "giving" storage to devices that can't physically have more storage, but they can utilize it over the network and it will be presented as local storage, which in some cases, some apps and services need (because they cant work with remote connections).