When you boot from SAN, you are only pulling the LUN down a single path. There is no multipathing at the BIOS level to help with failover. So if that path fails, the LUN goes away. I've read people saying that once the OS is up you can multipath, but I've never seen that actually implemented successfully. This is the major drawback for BfS and the reason I would never suggest it. You don't gain any performance in the OS doing that and you add a SPoF into the environment.
That's just my $0.02.
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"Only two things are infinite, the universe and human stupidity, and I'm not sure about the former."
Albert Einstein