On Thu, Jan 31, 2013 at 9:37 AM, Munir Nassar <tclug at beitsahour.net> wrote: > If linux crashed hard, it may not have had the ability to write to > disk. sometimes it is preceeded by oopses or non-fatal panics, but in > my experience not often enough. > This reminded me of something interesting I discovered accidentally a couple years ago. My employer at that time had a fibre channel fabric, connecting all of our headless servers to their storage. I was performing some maintenance on the switch fabric, the nature of which I can't remember at the moment, but regardless, it required me to disconnect a couple fiber patch cables. I pulled out one of the cables and then got distracted for a couple minutes by something else. During that time I started getting pages about a system being inaccessible. I started looking into the situation and quickly discovered that instead of disconnecting the cable I had intended to, I accidentally pulled the cable connecting this server to our FC network, effectively pulling its storage subsystem out from under its feet. I re-patched that cable, then pulled up this server's console, fully expecting to see a kernel panic. Instead of seeing that, I saw what appeared to be a completely functional system. Not believing what I was seeing, I checked the system's uptime and sure enough, it indeed had not rebooted, but rather just picked up right where it left off before. Armed with this information, I started playing around with a test system to see how long the kernel would stay alive with *no* storage connected, and was able to stretch things out well past the 15 minute mark with no ill effects. This all was a revelation to me, as I had always assumed that, absent a working root partition, the system would immediately crash. I now know that's not the case. Now, in this situation, the disks were connected via fibre, so there were no electrical/grounding ramifications to disconnecting while in use. I certainly would not advocate trying this on non-hotplug, electrically-connected hardware, as I'm sure you'd release the magic smoke from *some* component. :) -Erik -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mailman.mn-linux.org/pipermail/tclug-list/attachments/20130131/6e3fe297/attachment.html>