[NTLUG:Discuss] what companies are using linux in the dfw area?

[Steve Baker]

Robert Pearson wrote:
> Steve Baker wrote---
> 
>>All of the graphics boxes are diskless (for reasons of space, cost,
>> reliability, ease
>>of software maintenance, etc).
> 
> 
> How are you booting?

I'm not an expert on that aspect of our systems - but AFAIK, the BIOS has a
'boot from ethernet' option - it does some kind of DHCP access to get it's
IP address - and we use that to figure out which software/drivers/etc to send
it based on it's MAC address.   The PC's have to have a power-on-from-LAN
feature so we can turn them on remotely....I vaguely recall that we've had
problems finding the right kind of ethernet cards to do that properly.

But as I said - that whole aspect of the system is a bit of a black-box to
me.  Other people on the team understand that stuff - so I don't have to!

All of the diskless clients share a single copy of Linux on a special write-protected
partition of the server's disk drive - but each machine has an individual writable
partition that is mounted and used only by that machine.  Those partitions are *tiny*.

Once the machines have booted into the kernel, all subsequent disk I/O is via NFS.

> The smallest commercial boot kernel I have read about is Nitix Linux at 16 MB.

Yeah - I don't know what size ours is - it's a basic GenToo setup - but with everything
we don't need ripped out.  However, we have plenty of space in RAM and having a
microscopic kernel isn't by any means essential.

> What do you use for swap?

These machines have 2Gb of RAM and with the applications we run, they never
need to swap.   If we provide them a swap partition (and I'm not sure we do)
then they never do actually *use* it.

> What do you use for Storage?

These diskless nodes don't actually do much in the way of disk I/O once they
are booted and running the single application we give them on startup.   Anything
they do need to write (eg log files) goes via NFS onto their private partition of
the on the one PC on the network that has a disk.

This is not a particularly general-purpose computing machine - it's a single-purpose
'embedded application'.  The single application that they run is all there is.

Data is served to these applications via custom UDP protocol packets from our
own software.  Partly this is to allow us to use broadcast mode to send the
exact same data to all 40 machines in parallel.  The amount of bandwidth we
consume in doing that is already close to the practical limits of GHz ethernet
- so this kind of trickery is essential.

Some of our systems use a single vanilla 200Gb ATA or SATA drive for everything,
others have an off-the-shelf big-assed multi-terabyte RAID box.

> I am very interested in diskless environments. I am looking for
> someone who is willing to share their experience using something other
> than a disk to boot and swap. Such as CF (Compact Flash) to boot and
> possibly for swap. External boot and swap information would be
> appreciated.

We don't have any other storage than the single hard drive and main memory.

Part of the reason for doing that is that some of our flight sims are used
in highly classified military environments in which all non-volatile media
has to be unplugged and locked in a safe when the machine is not in use.

Having to unplug 40 of *anything* every evening and plug them all back
in again the next morning would be a massive pain - hence the desire to
limit non-volatile storage to a single sled-mounted hard drive.

However, there are other benefits too - being able to back up all 40
machines in one operation, being able to upgrade software on all 40
machines in one go...that kind of thing.   Hard drives are pretty
unreliable too - so reducing the number of them from 40+ to a single
drive improves overall system reliability quite a bit.

---------------------------- Steve Baker -------------------------
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