Allowing two Macs to see one share via fibrechannel

Question

Hi,
I would like to setup an xServe + XRAID to share one volume with two Macs. I thought I will be able to see/write/read to one drive from both machines using fibre channel cards in each Mac. I don't need to write at the same time to the same file. But I do need to connect to the same folder or drive and manipulate other files at the same time.
I am getting different answers from a couple of tech people. Some say it's impossible without Xsan and don't think other software solution is reliable enough. Apple Business sales person says it's possible. His solution is like so:
A. XRAID connected to Xserve via fibre card.
B. Xserve fitted with two fibre cards - one card connects with two cables to XRAID. The 2nd card connects via one cable to one G5 and via the 2nd cable to the 2nd G5.
So if I have only two machines that need high-speed connection to the raid I can avoid using a fibre switch and he promises this will work.
Anyone has a setup like this? If the above doesn't work what's my best solution. Is Charismac fibreshare a good solution compared to Xsan?
Any guidance will be appreciated.
Thanks in advance,
A.

Answer 1

It sounds like your Apple business sales person could
use a little education on the matter.
I'm confused and baffled on the suggestion to have 2
FC cards in the Xserve and use that for bridging. It
will not work, and it is not supported.
To have two Macs see the same volume, you need a
fibre channel switch. However, without software to
manage reading and writing, they will corrupt the
volume, as fibre channel is a block-level protocol,
and does not support locking primitives (file systems
like HFS+ support this for single machines, and
network file protocols like AFP, SMB, and NFS do it
for sharepoints and multiple machines).
So, for multiple systems to access the volume at the
same time, you need a SAN file system. Most of them
(Charismac's FibreShare, FibreJet, etc.) have "volume
level locking," which means one machine can write to
the volume at a time. This is the WHOLE volume, so
if one of the users is writing files, ANY files,
nobody else can do anything but read. This is a
pain, because if user #2 wants to write, an
administrator must remove user #1's write privileges
before he can write anything. Xsan is a "cluster
file system" and supports file-level locking, which
means you can do exactly what you want.
I will note, though, that Xsan is a bit complicated
to set up, and it really does demand you know what
you're doing, and that you "do it right." To set it
up right, you're talking a minimum of $30K in
equipment and software. You need a dedicated
metadata network, I STRONGLY recommend both a primary
and a backup metadata controller that do almost
nothing else (both would be Xserves), and you should
probably set up Open Directory as well, as it
simplifies things. So we're not talking easy here,
and we're not talking cheap (in the absolute sense of
the word -- though most of the solutions Xsan
competes with are 5 to 10 TIMES its cost).
So what do you get, then, with Xsan? You get
flexibility, and more importantly, you get SPEED. If
you are doing high definition video, with multiple
edit stations, then Xsan is your ticket to
salvation.
If you don't need Xsan's speed (and by speed, I mean
with HUGE, sequential files), then just setting up
AFP on an Xserve that's connected to an Xserve RAID
will give you very good performance (say, 50+
MB/sec), with none of the complexity, at
substantially lower cost. I didn't see your original
motivation for having the volume shared directly via
fibre -- what's driving it?
Thanks for your detailed response. I am learning a lot this week... I am baffled as to why an Apple certified person will claim we can connect two machines to see the same share. He also said that Xsan is needed only we want to work on the same file as the same time - not the same share. To answer your question: I was hoping to gain substansial speed improvement by switching our office from Ethernet to Fibre channel. We have an opportunity to upgrade our current system and have the budget for Xserve+xRaid. I was not aware of the file level limitation that fibre channel presents without Xsan. We do some video editing (DV only at the moment) but mostly graphic design (web+multimedia). We deal with large and small files on a daily basis. We currently share files via a simple NAS ethernet solution (infrant ReadyNAS) which provides reasonable performance. However I feel the system is lagging behind compared to having files stored on a local SATA drive. I was hoping that by investing close to $20K we will upgrade to larger, more durable drives as well benefit from faster connection. I also thought this will also allow us to edit from two or three stations directly to the RAID instead of sticking with one dedicated machine. I wanted the video files to be on one big share. so when an editor is done with final cut pro I can work on the same file in Motion or compress to Flash Video, etc. without copying to another drive.
To summarize I was hoping to create a simple NAS with faster speed. But the more I read about this it looks like we need Xsan but that it is too complicated for a small firm. We are also interested in xserve so we can work via ARD remotely if needed.
The way I see it we can do one of three things:
1. get Xserve+Xraid and have fibrechannel only between them. get a good gigabit router and have files shared by all. I don't know how much faster this will be compared to our current NAS solution but it sounds like we will see some improvement. (we currently all are on gigabit network but I am not sure if the router supports jumbo frames, if all the cables are right, etc.)
2. get Xserve+Xraid and have fibre channel between the two as well as add a fibre channel card card to one G5 tower. enjoy faster speed on that machine but dedicate a drive that is outside of the main NAS setup - do we need that for dv footage? perhaps just for capturing. It sounds like we can edit footage using ethernet connection but I am not sure if that will sustain capture rate.
3. risk it and follow what the apple rep said: try to see the share from two machines without fibre switch - either it works or return the extra fibre channel cards.
It sounds like the current version of Xsan is too complicated for us. The question is how much speed we can get via ethernet and should we try to make one machine a dedicated video unit.
Thanks.