[ntp:questions] Re: ntpd, boot time, and hot plugging

Richard B. Gilbert rgilbert88 at comcast.net
Thu Feb 3 22:14:26 UTC 2005

Brad Knowles wrote:

> At 10:21 AM -0500 2005-02-03, Tom Smith wrote:
>>>      With a decent drift file ...
>>  Precisely. The decent drift file is a problem. It sometimes doesn't
>>  exist after a large initial offset has been turned over to ntpd.
>     Even without a good drift file, you can still sync very quickly. 
> It may not be seven seconds, it may be fifteen.  But that should still 
> be tolerable.
>>  You should discuss that with a bank or stock exchange that
>>  is losing millions in transactions during those seconds
>>  or with public utility that is paying the government
>>  penalties for downtime. :-)
>     My wife is general counsel, head of legal, and secretary to the 
> board for the world's largest clearing and settlement firm for 
> European stocks and bonds, with an annual turnover in excess of 256 
> trillion Euro last year, and assets under management in excess of 
> twelve trillion Euros.  Yes, I mean trillion.
>     When Argentina decides not to make their interest payments on 
> their Brady bond debt, because 80% of their bonds are held through her 
> company, the final decision of whether or not to declare what used to 
> be the world's seventh largest economy officially bankrupt, arrives on 
> her desk.
>     I understand the scale of the problem.  With over a trillion Euro 
> of turnover in a single workday, milliseconds do count.
>>  Well, no. As David pointed out in his posting, all engineering
>>  is a matter of tradeoffs. For many users, the tradeoff needs
>>  to be 'Get these applications up fast on a "good enough"
>>  time and refine the time (and frequency) in the background.'
>     So, doing a single query and taking whatever bogus time may be set 
> from that server, is more important than waiting a few more seconds to 
> make sure that you've got a pretty good timesync?
>     I'm sorry, I don't buy it.  The bigger the application, the more 
> you have to lose, the more important it is to have good time sync.
>     See above -- milliseconds do count.
>>  Perhaps it is. For you. If it's seven seconds.
>     For financial applications, if the server goes down, then your N+M 
> fault-tolerant systems take over that load, and not a single 
> transaction is dropped or excessively delayed.  If your main server 
> facility is taken out by terrorists or natural disaster, then your hot 
> spare facility, that is located hundreds or thousands of miles away, 
> takes over and a few transactions might be delayed, but nothing is 
> dropped.
>     If you're running something that mission-critical and you don't 
> have those kinds of systems (which can tolerate a few extra seconds of 
> startup time in order to ensure that the time is set reasonably well), 
> then you are shooting yourself in the foot with a thermonuclear 
> weapon, and you will get what you deserve.
It's worth noting that, on September 11, 2001, Merrill-Lynch "failed 
over'" to a duplicate data center in Westchester County in something 
like four minutes; without losing a  single transaction or a byte of 
data.  If  downtime costs you $50,000,000/minute, the budget to ensure 
that there isn't any downtime is practically infinite!!!!!

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