nfs -- file creation ctime - NFS

This is a discussion on nfs -- file creation ctime - NFS ; FC> Furthermore, even synchronized time is not synchronized FC> to the precision of NFS timestamps. So not only is it not FC> realistic to assume "precisly synchronized time" (relative FC> to timestamp granularity), it is impossible. SR> How accurate are ...

+ Reply to Thread
Results 1 to 2 of 2

Thread: nfs -- file creation ctime

  1. nfs -- file creation ctime

    FC> Furthermore, even synchronized time is not synchronized
    FC> to the precision of NFS timestamps. So not only is it not
    FC> realistic to assume "precisly synchronized time" (relative
    FC> to timestamp granularity), it is impossible.

    SR> How accurate are network time servers?

    Are you asking how _accurate_ they are or how _precise_ they are?


  2. Re: nfs -- file creation ctime

    Guys,

    Is there a misunderstanding here? The time available to all system
    components ultimately comes from an atomic variable maintained by the
    kernel, usually in seconds and nanoseconds. The time and frequency of
    this variable is disciplined (sic) by NTP, either via another server or
    by a local reference clock. With respect to NTP, the precision is
    defined as the time to read the clock, usually the gettimeofday() or
    similar system call. In modern systems the precision is typically less
    than one microsecond. Note that the precision of the NTP timestamp
    itself is 232 picoseconds, or about 0.2 nanosecond.

    You ask about the accuracy of an NTP time server. This depends on a
    number of factors, machine room temperature variations, network delay
    variations, etc. With a GPS receiver and pulse-per-second (PPS) signal,
    typical accuracies are in the low tens of microseconds. Clients sharing
    a common Ethernet with such a server typically show errors less than 100
    microseconds. Conventional wisdom suggests better than 1 ms for campus
    networks, better than 10 ms with fast Internet connections and better
    than 50 ms in all but really broken paths.

    Much more information is available at www.ntp.org.

    Dave

    J de Boyne Pollard wrote:

    > FC> Furthermore, even synchronized time is not synchronized
    > FC> to the precision of NFS timestamps. So not only is it not
    > FC> realistic to assume "precisly synchronized time" (relative
    > FC> to timestamp granularity), it is impossible.
    >
    > SR> How accurate are network time servers?
    >
    > Are you asking how _accurate_ they are or how _precise_ they are?
    >


+ Reply to Thread