So I am an Xsan salty dog and I will tell you that I understand what you want and I understand why you want it... But you better have a budget of at least $40,000.
I will explain.
Yes Xsan is "free" when you buy a Mac mini. But just because the StorNext implementation on OS X is not directly charged for, does not mean that you get a SAN for free. You have a lot of requirements to make this work. Both hardware and infrastructure. Here is what you would need for the absolute bare minimum of a setup.
Two Mac mini Servers - one to act as primary metadata controller and the second as a backup metadata controller. You really don't want to run Xsan with a single controller. Yes, you can use a workstation as the backup but if you frequently restart that workstation you are going to have a headache. Best to dedicate at least two devices for metadata control. Cost, ~$2400 (assuming AppleCare and extra RAM)
New workstations that have Thunderbolt - Your 2009 iMac is out in the cold. Time to upgrade. But realize the iMac is due for a refresh. Plus the Mac Pro is coming later this year. Both systems will have significant performance improvements over existing systems. Budget about $3200 for an iMac with appropriate RAM and storage.
Promise SAN Link Adaptors (or competing Thunderbolt to Fibre Channel bridge) - one for each of the controllers and one for each connected workstation that does not have a PCI slot. So if you have two mini's and an iMac, then you need 3. They are about 600 each last check. Total $1800.
Fibre Channel Storage - To run Xsan, your storage must be on the FC bus. You can not use Thunderbolt, Firewire, or USB storage. You must get a FC array. Apple certified Promise vTrak. Now that Active is dead, they are really the only ones to trust. But even the smallest array will set you back $20,000. However, to build it right, you should be building in increments of 4 LUNs. That means two arrays. Can you get away with one, yes. But you are still looking at $20,000 minimum.
Now, you need to connect it all together. You will need a Fibre Channel switch. If you get an 8gig switch, only the storage can connect at full speed. Recall that the SanLink adapters can only run at 4gig FC. (4 + 4 = 8 and TB is 10 total). Now Thunderbolt 2 has been announced so it may have a new SAN link that can accept 8gig FC. So you may want get a Qlogic 5600 series for about $2200 or a Qlogic 5800 series for about $4500. In most environments you buy two of these and then spit all devices across the two fabrics for redundancy.
Next, you need two ethernet networks. This means one network for internet and one network dedicated just to metadata between all SAN connected devices. So two 1000 base switches. You can probably cheap out on this due to your size but still, this will be a few hunders dollars. But, aha, now you need to make a second ethernet connection on all the devices. You will need a thunderbolt to ehternet adaptor or a usb to ethernet adaptor. Each is, what, $40? So 2 controllers and one workstation is $120.
Next, you need wiring. You will need to run fiber and ethernet (2 per device) to connect everything together. You will likely not be running in your walls so you save on jacks and faceplates, but you still need some patch cabled. This is both FC and copper ethernet. There is another $200.
Ok, so that builds you a 2 controller, single workstation Xsan. But your job does not end there. You should also be looking at uniterruptible power (get at least a 1500 VA system for each mini - this ensures you don't need to call an electrician, another for the FC Storage, and another for the FC switches and ethernet switches.
And now, what about backup? If you get big storage (an X30 can start at 32 TB of storage) you need big backup. Don't trust your data to Xsan alone. If you have trouble, kiss your data goodbye.
So, still want to do it?
Xsan is, and has been, an exceptional product for the right environment. Apple is still actively developing the product (10.8.4 had a hug update and 10.8.5 just included some more stability fixes). Plus, Quantum is moving forward and those advanced trickly down to the Mac. But there is a high cost of entry.
I am thinking you might simply want to wait and see what the new Mac Pro has to offer. You 2009 iMac is holding you back. It has no TB, has a slow internal HD and i/o bus, and you are limited by your external drive options. The new Pro will intro TB 2, third parties will have storage available, and maybe, just maybe, Apple will convert Xsan over the TB storage. The specification and the implementation shows that we can push multiple protocols over the bus. Maybe it is just a matter of time.
Hope this helps. I feel your pain.
And "WOW" means both ultimate cost of solution and detail of answer. Thanks a lot for such useful and detailed explanation)
Now I have no doubts that SAN isnt suitable for me) You right (and I also have same idea) that Mac Pro is best way. I also reconstructed my home network, so now I have 3 Tb Raid-1 WD external drive for photo/video and nothing more. I'm planning to upgrade it to Thunderbolt drive. I desided to refuse from massive storages like Areca or Pegasus, because 3-4Tb is enough and I dont need RAID-5 or so. On WD I have RAID-1 and it also backs up with Time Machine and Bitcasa. So I have 2 backup copies.
Of course I have to plug WD to iMac for editing and then to Mac mini for render, but I think with Mac Pro slow-render problem will be gone.
All my media is now stored on Mac mini, so I have anywhere access to it.
I have only one additional question - what do you think about globalSAN/Xtarget? According to their website it's very interesting software, and I could get something like home SAN just for ~1500$. But how good is it?
I will admit not having extensive experience with the lower end SAN products. I tried the TigerSAN and a few of the other variants a few years ago but ran into all sorts of compatibility and performance issues. Luckily, this was all in the lab and no customers were harmed in the testing I would expect these products have developed since. However, the shops I support have the budgets and the size to build out Xsan so I've not been actively investigating alternatives.
I have been watching the development of http://www.studionetworksolutions.com/evo/ recently. They announced the latest version this week at IBC. They may be on to something with this approach as a means of powering small shops with a self contained unit that actually works toward Final Cut compatibility.
Here's to the new Mac Pro. Can't come out soon enough.