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Date:      Mon, 6 Dec 1999 11:12:21 -0800 (PST)
From:      Matthew Dillon <dillon@apollo.backplane.com>
To:        Dan Nelson <dnelson@emsphone.com>
Cc:        current@FreeBSD.ORG
Subject:   Re: NFS client zeroing out blocks on write?
Message-ID:  <199912061912.LAA71576@apollo.backplane.com>
References:  <19991203112518.A43843@dan.emsphone.com> <199912042051.MAA56920@apollo.backplane.com> <19991205024034.A77822@dan.emsphone.com>

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:
:In the last episode (Dec 04), Matthew Dillon said:
:> Hmm.  I thought we had fixed all the zeroing problems.  Are you sure
:> you compiled your current up from the latest source?
:
:Yep.  The machine was a snapshot install from Nov 15 that I rebuilt
:world on the 23rd, and rebuilt the kernel on Dec 2nd.
: 
:> I am presuming there are no other clients accessing the output files
:> while the split is running?
:
:Correct.  "split" isn't even strictly necessary, but it makes it easier
:to generate multiple gigs worth of data across an nfsv2 mount point. 
:Depending on my mount options, the glitch is sometimes infrequent
:enough to only occur once every 5-10 gig of generated data..
:
:> Interesting.  It looks very similar to a problem we fixed months ago.
:> That problem was related only to NFSv3 and mmap(), and you aren't
:> using mmap() here.  It's disturbing to see this problem occur with
:> both NFSv2 and NFSv3.
:> 
:> I wonder if the problem occurs between a FreeBSD client and server.
:
:Most of my tests have been done on NFSv3 mounts since they are so much
:faster.  I'll try another test run, NFSv2 mounting another FreeBSD box
:and see what happens.
: 
:-- 
:	Dan Nelson
:	dnelson@emsphone.com

    Dan, I know this may be placing an undue burden on you, but can you try
    installing a 3.x snapshot to see if the bug exists there?  If the bug
    exists in 3.x then I'll know that it isn't due to changes I've made
    in 4.x (or at least not likely due to those changes).  If the bug does
    not exist then it gives me a place to start looking.

    The weird thing is that we are talking about a single process here, and
    I would expect this type of bug to occur with multiple contending 
    processes.    If it had just been an NFSv3 mount I would have suspected
    the commit rpc code, but if it is occuring on NFSv2 as well it kinda sounds
    like a preexisting bug that has just been brought out into the light
    due to changes in the way NFS works (major NFS performance improvements
    have been made in -current, for example, that allow NFS to saturate the
    network more easily).

					-Matt
					Matthew Dillon 
					<dillon@backplane.com>


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