I know the topic is quite unusual, so I will explain in simple as possible but in detail...
I know this is possible, but I just don't know how to do or what to use. I been googling for weeks and tried many tutorials or forums out there, but I couldn't get to where I want to do...

I run an internet/LAN cafe. I want all my client computer to be boot off the network using iscsi & gpxe, so I can avoid hardisk crash/dead..
I can do this easily for single PC to run windows xp. But if I tried booting more PC and booting windows xp from single iscsi image, the image file will get corrupted, because many connections to single file.
I set the image file to read-only and also tried cluster filesystem, OCFS2, but i'm not going anywhere. I'm stuck at booting many machines using single image file.

The reason i wanted to get all my PC to boot windows xp using single file is because I want to save time installing updates/doing same tasks for every machine. At the same time saving expenses for new hardisk if I use real hardisk for every PC.

I have idea to solve this, but I just dont know how to do it. It's like this...
If there is iscsi request to the image, the system will cache the write request for every PC to each PC cache file. For example; if I booting PC01 to PC05 at the same time, and yes booting from single image.
The system will cache the write request to file located: /iscsicache/pc01,/iscsicache/pc02,/iscsicache/pc03,/iscsicache/pc04,/iscsicache/pc05 or maybe using ipaddress is simpler or easier to find...
No write request to the image file, but all write request will be directed to each cache files, labeled with client's ip address or hostname.

And yes, the read request for each client will be the same. From image file+cache file

I'm quiet new with linux, but I like to explore and linux seems to be very interesting for me bcos it's like there is no boundary so you can do many things as long as you know what to do

Sorry for my english and correct me if i'm wrong for my idea, not my english(I dont want to discuss it here, r u?)
Any opinions is welcome, please