A few questions of varying difficulty

[sretalla]

Depending on your real aim, ln -s (symbolic linking) can probably get you what you want... if I try to show an example below, maybe you can see what I mean:

Code:

mkdir /mnt/vol1/documents
mkdir /mnt/vol2/files
mkdir /mnt/vol3/master  #this can really be wherever you want, but should not be a sub-directory of the other locations you are going to link... you don't want to create a recursive, circular link.

cd /mnt/vol3/master
ln -s /mnt/vol1/documents/ documents/
ln -s /mnt/vol2/files/ files/

Should result in:

/mnt/vol3/master/

containing "documents" and "files" and appearing to be a single drive for all practical purposes (including SMB sharing and whatever else)

You need to take care and do a bit of reading about how some applications work with symbolic links... sometimes backup software might just backup the link itself, but it can be instructed to "follow links" so that it will backup the entire contents of the linked locations... just one example where it needs attention.

 

[sretalla]

An interesting/important additional note...

Although perhaps obvious, it's worth saying that each folder that is linked is limited to the capacity issues of the pool it's really located on. Linking doesn't magically share the whole capacity of both (or however many) pools in both directions... sorry, no miracles here. ;)

Just to spell it out from the example above:

if
/mnt/vol1/documents is in a pool with 10TB
/mnt/vol2/files is in a pool with 5TB
/mnt/vol3/master is in a pool with 20MB (note MB here, links are very small, so you don't even need 1GB of space if all you will store is links)

If you think about the space on master (overall), you could store 15TB (although this would put you at 100% of pool capacity, so you shouldn't...)

But if you needed to put more than 5TB in files, then you're going to be stuck as vol2 is where you're keeping it (or even more than 4TB to stay under 80% as recommended).

I'll stop here as I guess everybody is now following my meaning.