iSCSI Lun

[F1ydave]

iSCSI LUN first timer here!

I am running EXSi 6.0 u2, mainly hosts a Windows Server. I have an Asustor NAS running a plex and backups for my server. The NAS is setup as two raid 5's at 7tb each (6 drives). It can't handle the transcoding of larger 1080p videos with AAC audio. I was thinking about tossing it on a VM on Ubuntu and trying out iSCSI LUN's.

I dont know much about LUN.

Would I be able to access the LUN from Ubunto/Plex for a media storage? Would I be able to access it with Windows Server? Should I add it to the Esxi datastore?

I have tried reading up on iSCSI LUN but it is a bit confusing. Does anyone have a good guide or advice?

How do you set it up properly as a storage device? Is best practice to have multiple LUN's between operating systems? What about sharing a LUN to a small group of devices, say 4 or 5? If I added a LUN to windows 7, is that too considered a 'initiator'?

This helped me out a bit, maybe someone can fill in the gaps?
<!--:Tr-->ISCSI Nedir Ve Nasıl Oluşturulur<!--:--><!--:en-->What is ISCSI and How to Create & Use<!--:-->

 

[MiniKnight]

Ok so you have two objectives.

• Faster storage for transcoding - I'm reading that the storage is not fast enough, not CPU bound
• Learn about iSCSI

Is that correct?

I would not try using iSCSI for home media transcoding. It's much easier to just use a samba share or something like that. Maybe try a journaling SSD to improve performance if that's possible on the Asustor.

On the iSCSI here's the absolute basics. Hoping this mini-novella will get your understanding OK around iSCSI to the point you can use it.

iSCSI Target = Target of the SCSI commands (disks). So the iSCSI target is what you run on the server with disks
iSCSI Initiator = Machine that wants to initiate a connection to the iSCSI target and send SCSI commands

Now here's the trick. Unlike with a normal NFS/ CIFS share where you are mapping directories, the Initiator is likely going to be determining the file system and such on the iSCSI share. It's like plugging in an unformatted disk into a server/ PC.

LUN = an individually addressable devices. So, you have a RAID array on the Target. You then want to parse out chunks, say 500GB to multiple machines. The LUN is more or less what says you have a 500GB SCSI Disk 0, 500GB SCSI Disk 1, 500GB SCSI Disk 2. You then can have Initiator 0 connect to Target 0 and use the LUN for Disk 0 and Disk 1. Initiator 1 can connect to Target 0 and Connect to Disk 2.

NFS /CIFS you can say go do directory0, directory1, and directory2 but remember, iSCSI is more like raw disks and you need to ensure the right machine is getting to the right disk, using the LUN.

Basically, most people hate LUNs. They serve a purpose but IQNs and LUNs are a total pain, especially as you get large storage systems. There are entire companies and software products which are in essence a way to manage LUNs.

Virtual machines/ hypervisor nodes are a great use for iSCSI/ LUNs. You can have a light local disk configuration then map iSCSI LUNs over a network to "add" disks without having to physically put a disk in the machine/ VM. If you're trying to have a repository to store stuff where you want multiple clients to access, NFS/ CIFS are better.

 

[EffrafaxOfWug]

Aye I think this'd be better split into two threads, one for transcoding and one for the iSCSI stuff.

Transcoding-wise you're almost always going to be CPU limited. Even high bitrate 4k stuff will barely tickle a RAID array in terms of reads. There's some things that'll use hardware gubbins like Intel QuickSync to accelerate transcoding but think those are few and far between.

As MiniKnight points out, presenting an iSCSI LUN from your NAS is basically like having a hard drive plugged in via a network cable; you can address it from multiple devices, but only if it's got a filesystem that can handle reads and writes from multiple devices - most can't. It's useful for things like ESX because VMFS is multiple-device-aware so the same storage can be visible across multiple devices (although only actively in use by one) but for most work you're much better served by using file sharing a la CIFS or NFS.