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Re: High-Precision NFS Timestamps


From: Eric Reischer
Subject: Re: High-Precision NFS Timestamps
Date: Thu, 13 Jan 2011 09:28:20 -0500
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.16) Gecko/20101226 Iceowl/1.0b1 Icedove/3.0.11

As I said, we do use NTP to keep our machines in synchronization, every hour. However, there's no time client that will keep everything aligned up to the nanosecond level, which is what ext4 timestamps are in. Besides, any amount of network lag is going to introduce small errors in this anyway. The only temporary solution I can think of is to force the clock on the NFS server to be ~1 second behind all of the clients, so timestamps will never appear to be in the future. Not a clean workaround, but it appears there's no other stopgap solution.

On 01/12/2011 09:58 PM, Bob Friesenhahn wrote:
On Wed, 12 Jan 2011, Eric Reischer wrote:

I recently upgraded our NFS fileserver to an ext4 filesystem, and since then we've been having clock skew warnings from make (3.81). Because the ext3 filesystem that was previously running on the NFS server didn't support high-precision timestamps, we didn't have clock skew warnings because an hourly cron job kept the clocks in relatively close sync. However, since ext4 does support sub-second timestamps, we're getting warnings about clock skews on the order of a few milliseconds. I tried adding our target objects

Usually the solution to this is to install and run ntp (Network Time Protocol, as offered by 'xntp') on the machines on your network. This seems to be quite effective on real hardware, and sometimes less effective in virtual machines (e.g. VMWare or Virtualbox) which can only emulate the hardware clock. I am not aware of a more effective method than using ntp.

Bob



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