From: "Gregory Baker" <gregory.baker@amd.com>
Subject: bug in linux mount? (says NetApp)
Date: Tue, 11 Jul 2006 14:00:23 -0500
Message-ID: <44B3F547.9010507@amd.com>
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Cc: autofs@linux.kernel.org
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We have thousands of linux clients hitting netapp file servers (many 
3500 series, clustered) on a local gigabit LAN.  From time to time, 
applications return "file not found" when attempting to automount a 
directory and access a file.  An example of this is a long running 
process, which reads in data, processes it for hours (in which time the 
filesystem is unmounted) then tries to read more data from that mount 
point (which causes a "file not found" error in the application).  This 
occurs about 1/100th of the time.

Researching at Netapp turns up this bit by Chuck Lever (Linux NFS 
contributer)

"Using the Linux NFS Client with Network Appliance Filers"
http://www.netapp.com/libr ary/tr/3183.pdf  (February 2006)

page 10 says...

"Due to a bug in the mount command, the default retransmission timeout 
value on Linux for NFS over TCP is quite small...To obtain standard 
behavior, we strongly recommend using "timeo=600, retrans=2" explicitly 
when mounting via TCP."

Our defaults (assuming man pages are correct, RedHat Enterprise Linux 3) 
would be timeo=7, retrans=3, which translates to 7+14+28+56 = 105 tenths 
of a second (10 seconds).  It appears netapp is suggesting waiting 
600+600 = 1200 tenths (120 seconds) before giving up on the mount command...

* What "bug" in the mount command do you believe NetApp is talking about?

* What do you think proper options for NFS auto/mounts would be for 
extremely busy centralized NFS filers?

* What is the reference standard behavior?

Thanks,

--Greg

-- 
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Greg Baker                                         512-602-3287 (work)
gregory.baker@amd.com                              512-602-6970 (fax)
5900 E. Ben White Blvd MS 626                      512-555-1212 (info)
Austin, TX 78741


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