iSCSI - Who has used it?

[Kurtois]

I went the expensive route and purchased a Synology NAS over going with FreeNAS. That said, I am curious if anyone out there has experience with the iSCSI protocol. 

[Chris Weiss]

I've built my own target using debian and scst-iscsi, and use it with
linux and esxi initiators.

[Joseph^2]

Stache and I work for a place that makes an initiator for mac. Our flagship is a large SAN system. What do you need to know?

[Kurtois]

Thank you for chiming in. I really could use some help.

I have several questions, actually. 

I am familiar with the place that makes, what seems to be, the most popular iSCSI initiator for the OS X platform and read that they are here in Saint Louis. Unfortunately, at $89 a pop now (was free) for a single machine license, seems that I must weigh more heavily the pros/cons of the situation. I am a home user and am not using this for a business.

That said…

iSCSI seems attractive because the MacOS (OS X 10.8) clients see the iSCSI storage as local storage; this does not seem to cause much issue for OS X, that I have read about, anyway.

Goal:

Provide HFS+ file system to OS X client machines such that they interact with the iSCSI storage as if it were a directly connected mass storage device.

It would be *NICE* to access the same home folder on multiple machines, however, I don't think this is possible.

Notes/Concerns:

-I have read that more than one client cannot connect to an iSCSI LUN (correct terminology?). This means one client would have to unmount a LUN and then reconnect on a different client.

-There will only be one physical user of the Synology NAS, however, if I have to remember to mount/unmount a LUN, that does not sound appealing.

-I have read thoroughly the Synology produced wiki and scoured the web for help with this. 

Facts:

-I am using a Synology NAS (DS413) with 4 2TB WD RED NAS drives being accessed on the same LAN by three OS X 10.8 clients.

-I created multiple volumes on RAID 

-I created two disk groups (one for Time Machine backups from two client machines; hard drive size of clients - 128GB and 500GB)

-RAID type: Synology Hybrid RAID (SHR) with 1 disk fault-tolerance

-I have two disk groups currently; one that has 1.5GB allocated, the other 5TB.

From my reading, it seems as though I need to have one volume dedicated for Time Machine backups with room for expansion (how much?). Another volume created for whatever else I want to store.

Preface Questions:

P1.

Does iSCSI make sense for a home user? I will be using the NAS as an iTunes server, surveillance system, Squeezebox server, in addition to doing specific file storage (photos, PDFs, movies).

Questions:

Q1.

How do I determine if I want a file-level or block-level iSCSI LUN?

Q2.

Would it be best to create one LUN per client machine?

Q3.

How does one expand an iSCSI LUN once created?

Low Priority Questions:

LP1.

Compare LUN snapshots and LUN clones (perhaps a link here is best).

[Joseph^2]

That is where we work. You can still get globalSAN v.3 for free. It just does not work on 10.7 or 10.8. We had to completely rewrite the initiator to work on x64 OSX. If you want to run the trial, it will let you connect to one target.

There are certain softwares that will not let you use NAS as storage for project files (although that is thankfully in its final days). Another reason to use iSCSI is that it is much lower latency than SMB and AFP.

Accessing block storage from multiple machines at once is a bad idea. Unless you are using some kind of access management or network-aware filesystem, you should avoid sharing iSCSI storage.  This is why we have SANmp, which provides volume-level control of SAN mounts. Our software allows multiple RO and one RW mount per volume.  The user and mount info are stored to the LUNs and there is no need for a metadata controller. Other SAN management software provides locking per-file, but that level of control does require a metadata controller. 

That said, there is nothing blocking you from mounting a LUN with multiple initiators. The problem lies with the fact that HFS and NTFS were not developed to handle multiple writers.

We have a lot of users using Synology systems. Our forums (http://www.snsforums.com/) and those at creative cow will likely be of help.

Some other things to keep in mind:

SAN storage does not do well with sleep.
Spotlight causes issues with SAN volumes when mounting and unmounting.

Notes/Concerns:
-I have read that more than one client cannot connect to an iSCSI LUN (correct terminology?). This means one client would have to unmount a LUN and then reconnect on a different client.

>You have likely stumbled on some discussion regarding the problems with multiple block-level writers.

-There will only be one physical user of the Synology NAS, however, if I have to remember to mount/unmount a LUN, that does not sound appealing.

>You can set up persistent targets with the MS-iSCSI and globalSAN iSCSI initiators. SANmp can be scripted, and there are automatic mounting tools for many other management systems.

-I have read thoroughly the Synology produced wiki and scoured the web for help with this.

>I'm sorry:) Synology support can be difficult to get. They have been pretty agreeable about working out issues with us, but we have better contacts there than most.

Facts:
-I am using a Synology NAS (DS413) with 4 2TB WD RED NAS drives being accessed on the same LAN by three OS X 10.8 clients.

>sounds ok

-I created multiple volumes on RAID

>sounds ok

-I created two disk groups (one for Time Machine backups from two client machines; hard drive size of clients - 128GB and 500GB)

>sounds ok

-RAID type: Synology Hybrid RAID (SHR) with 1 disk fault-tolerance

>good idea, but remember - raid is not a backup system and fault-tolerance only protects you from the loss of a disk, not dirty filesystems.

-I have two disk groups currently; one that has 1.5GB allocated, the other 5TB.

>should be fine

From what I know of recommended best practices for setting up time machine backups, you have the right idea. The size you need is determined by how much space you use, and how often you change files. To start, I would make sure you have about double the space you are using.

Preface Questions:

P1.
Does iSCSI make sense for a home user? I will be using the NAS as an iTunes server, surveillance system, Squeezebox server, in addition to doing specific file storage (photos, PDFs, movies).

>It can make sense, but it can be expensive for certain parts. If you stick to open-source initiators, clients, and use network-aware filesystem, its free!  The short of it is, unless you need the higher throughput, NAS is easier and it is multi-writer.

Questions:

Q1.
How do I determine if I want a file-level or block-level iSCSI LUN?

>You do not have a choice. iSCSI is block level.  There are some systems that try to virtualise that behavior, but the initiator + filesystem will not know the difference.
There is a situation where you can have have the target system internally mount SAN shares, and then reshare them over NAS. In this case, only one of the two systems should be allowed RW access.  We have a function set up like this on our "EVO" system, but it relies on SANmp.

Q2.
Would it be best to create one LUN per client machine?

Without SAN management, this is very likely the best option.

Q3.
How does one expand an iSCSI LUN once created?

If the target system allows you to grow the LUN, and you have tools to resize the partition on your initiator, and the management system does not get mangled, you are in luck. We are still struggling to get SANmp to work properly in this situation. We have only added the needed functionality to EVO, so SANmp will be next.
Resizing complex RAID systems can be tricky. 

Low Priority Questions:

LP1.
Compare LUN snapshots and LUN clones (perhaps a link here is best).

We really don't mess with these.  A great deal of our clients use backup and archive systems from different vendors, so we just try to keep things as non-proprietary as possible. If you are to use clones, you will need to have the max filespace available for each clone (unless you are attempting compression). Filespace needed for snapshots will likely depend on how often you change files.

If it is an option, AFP does do very well, and seems to scale with added bandwidth. For instance,  AFP over 10GbE has produced some nice results, whereas SMB seemed to be capped at the same speed.  That said, even with iSCSI, we have not seen 10GbE really outperform 4GbFC.

Unless there is some restriction, for your situation, I would stick with NAS.

IF you have more questions, please hit me up at joseph....@gmail.com

[Chris Weiss]

ISCSI really only makes sense if you are dedicating one per client due
to client local storage limitations, or if you are using a clustering
filesystem such as OCFS or GFS.

I'd seriously consider just using NFS. OSX supports it and you can
have as many pc's connected as you want. you can also share the same
directories out over SMB/CIFS to windows clients. There are very few
things you can't do on NFS.

[Kurtois]

Part of my thought on deciding to go with iSCSI for my Macintosh client machines was that I am considering setting up an OS X server. I read somewhere that if I used iSCSI, I could make applications happy using their "native" filesystem, HFS+. It would be "a nice to have" to have my home directory available to me when I login.

However, the initiator mentioned above for OS X clients is $89. That is a lot, in my opinion.