I think that you will hit the network limitations well before the drives become an issue. Depending on file sizes uploading just 30GB (1gb each) to the server even with teamed links is going to take ages. With the proposed setup you may end up wasting about a large chunk of the lesson just downloading and uploading.
Data transfer rate conversion online.
Looking at the client side limitations with a perfect back end system:
1GBit/s = 119.2 Megabytes/s * 50% (average throughput plus network protocol overhead) = 59.6 Megabytes/s
1024 megabytes / 59.6 Megabytes/s = 34.59s which is alright but assumes perfect network conditions and no additional hardware bottlenecks.
Looking at this from the server side however:
2GBit/s = 238.4 Megabytes/s * 50% (average throughput plus network protocol overhead) = 119.2 Megabytes/s
30720 megabytes / 119.2 Megabytes/s = 257.71s (4m17s) which is alright but assumes perfect network conditions and no additional hardware bottlenecks so your SAN should have lots of SATA disks to support this.
Add in the additional time taken to service 30 seporate requests and you are easily looking at 5min each way for each client. I guess it depends on how long your lessons are and a lot on how able the xraid is but best case you are probably looking at an average of 10 minutes of each lesson just for the copying let alone the logon and off time.
You could possibly add more ports to the xraid but whether this would scale depends on the harware of the xraid and the number and speed of sata drives along with the switching capacity of the networking hardware in the middle.
It can be done but you'd have to spend a LOT of money on the storage and network infrastructure.
Firstly, spindle quantity will be king.
I would suggest 2 x Sun 7110 SANs as they are buy one get one free. Set one of them up as the initial video staging area with all 14 disks in Raid0. Set the other up as a Raid5 mirror which archived the data off the Raid0 SAN every night. You'd also need to go 10GBE between the two SANS and 10GBE all the way to the Video Editing Suite with 1GB link per client. Of course that only actually gives you 2TB of editing space and 1.8GB of archive storage which probably won't be enough - but it'll be damn fast and good value for around £12k list price all in with the networking
If money's no object look at something like a Sun 7210 SAN - 47 x 500GB SATA disks set up in Raid 10 to give just inder 6GB of storage, AND these models come with an 18GB Solid State Flash Accelerator and 64GB of ram which will mean the server should be able to cache a fair chunk of the video being sent back and fore. The price will be Juicy though - £55k list price for the storage server (though I dare say Andy at Cutter Project could knock a few grand off that for you) + the 10GBE stuff. Ouch! Maybe this post should be in the blue skies section?