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List:       freebsd-hackers
Subject:    Re: OS support for fault tolerance
From:       Adam Vande More <amvandemore () gmail ! com>
Date:       2012-02-24 21:28:50
Message-ID: CA+tpaK2c3AjUF+my5=52xOHEFq0Q2a3nwXJKkfrjbhN4vQAv7A () mail ! gmail ! com
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On Fri, Feb 24, 2012 at 3:10 PM, Dieter BSD <dieterbsd@engineer.com> wrote:

> Depends on what sort of work the machine is doing.  If the job is
> something that can be done again, you could simply try again, if
> you still get different answers try a third machine or wade in and
> start manually inspecting things until you find the problem.
> If the job is time critical or you can't get the same inputs again,
> then the machine needs to get it right the first time.  How many
> 9s of reliability do you need and how many resources can you throw
> at it?  2x hardware can be good for better than 5 9s. (high quality
> hardware and software, and technicians standing by with cold spares)
> I've heard that mil gear uses 3x hardware.
>
> Building a 5 9s system is... non-trivial.  So I'm wondering what sort
> of reliability we can get with 2x off the shelf commodity hardware
> and a bit of software?  Similar to mirroring/RAID but with whole
> computers rather than just disks.  Classic Unix technique of doing
> 10-20% of the work and getting 80-90% of the result.
>

I don't have anything particularly insightful to add to this conversation,
but it is something I've looked into a bit.  The solution which seemed most
promising to me is Remus.  I don't know if any have heard of it so I offer
a link:

http://static.usenix.org/event/nsdi08/tech/full_papers/cully/cully_html/

I understand this doesn't correlate exactly with the OP's point but there
is good material there regardless.

-- 
Adam Vande More
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