On 27 January 2015 at 23:03, Warner Losh <[email protected]> wrote: ... > A "cold spare" that's sitting on the shelf powered off for more than 6 months. When > the original fails, the hot spare is returned to service and must wait an additional ~30 > minutes to get the latest almanac before it can recover UTC time from GPS time. > This 30 minutes of down time puts the system at < 4 9's of reliability, and is an > unacceptable delay. ...
That assumes you can instantly get the cold unit off the shelf and plugged in. I suspect that actually doing that will, in most cases, take well over half an hour, and hence there goes your 4 9's, regardless of how quickly the unit can give an accurate output.
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