iSCSi Volume vs LUN

[Insomniator]

So work bought me a Synology 1813+ NAS w/8 4TB drives for various needs around here. When I set it up it automatically created 1 huge volume with their hybrid raid system. I'm not worried about redundancy at the moment so whatever that is is fine.

I have almost zero experience with iscsi and my main question comes now down to volumes vs LUNs. It looks like I can chop this volume up into LUNs that show up as partitions in windows disk management. I have two servers I need to connect to it so I created 2 LUNS, and both servers can see both. I made one online on each and left the other offline to prevent data corruption.

However, the other guy here that knows about iscsi (configures and manages the network SAN's) says I have it backwards, that I'm supposed to create multiple volumes to attach to each server. I feel like the terminology might just be mixed up between us. Is the idea that multiple volumes would allow me to have different RAID setups based on need? Is there some reason to use multiple volumes instead of multiple LUN's?

Then comes the next part, targets. I have both LUN's mapped to 1 target, no chap/security enabled. If I created a second target I supposed I could enable CHAP and have different passwords for each correct?

 

[dave_the_nerd]

So work bought me a Synology 1813+ NAS w/8 4TB drives for various needs around here. When I set it up it automatically created 1 huge volume with their hybrid raid system. I'm not worried about redundancy at the moment so whatever that is is fine.

I have almost zero experience with iscsi and my main question comes now down to volumes vs LUNs. It looks like I can chop this volume up into LUNs that show up as partitions in windows disk management. I have two servers I need to connect to it so I created 2 LUNS, and both servers can see both. I made one online on each and left the other offline to prevent data corruption.

Your Synology sees one big volume, yes. It will chop that into LUNs that get assigned to client computers. (Initiators).

Because each LUN is then presented to a client machine (server) as a locally-attached disk, you can't have them sharing. (They'll overwrite each others' data. I did it for kicks in class last semester, actually.) Basically, the server doesn't know that the other server is accessing the virtualized disk, and doesn't get informed of new data in the space it thought was blank, so it does its thing. Meanwhile, the Synology is being told "write to block X" by two different servers, and does it, because you told it to pay attention to commands from both servers.

However, the other guy here that knows about iscsi (configures and manages the network SAN's) says I have it backwards, that I'm supposed to create multiple volumes to attach to each server.

Yes.

I feel like the terminology might just be mixed up between us.

Only inasmuch as the servers see a LUN as a single local volume, and your Synology sees its storage pool as a single local volume. They're the same thing.

I feel slightly dickish doing this, but reading this may help.

http://en.wikipedia.org/wiki/ISCSI

You'll note they don't actually use the word "volume" anywhere, really. The storage on the Synology (the "iSCSI Target") is the "storage pool." The servers connect to a LUN (provisioned out of the pool) using an "initiator."

Since different things are "volumes" depending on who's looking at it, that's a dangerous word.

Is the idea that multiple volumes would allow me to have different RAID setups based on need?

No need. Yes, you could present two or more LUNs to an initiator (server) and then software RAID them in the OS, but... why? The Synology is already running in RAID, so you're already realizing the full benefit of the striping/mirroring/whatever you're doing.

Is there some reason to use multiple volumes instead of multiple LUN's?

Multiple LUNs on the Synology => Multiple volumes on servers.

Then comes the next part, targets. I have both LUN's mapped to 1 target, no chap/security enabled. If I created a second target I supposed I could enable CHAP and have different passwords for each correct?

Your iSCSI target is the Synology box. Mapping both LUNs to the same target is sensible. (You don't have another one.)

If you trust your internal network security, etc., (maybe you're on a private VLAN?) then you can probably chug along without authentication enabled and not worry about it.

Ideally, I'd probably have two LUNs - one for each server - and then two more sparse clones for recovery purposes.