[Bug 1903974] Re: issue reading netcdf4 files with nfs v3 on ubuntu 20.04

[Balagopal Pillai]

The test is done with a netcdf4 file from here -
http://rain.ucis.dal.ca/ctm/GEOS_0.5x0.625_NA.d/MERRA2/1980/01/MERRA2.19800101.A1.05x0625.NA.nc4


>From 20.04 nfs server

v3 mount test -   mount -t nfs -o vers=3  192.168.1.225:/nfs /tmp/test/

ncdump  -h -s MERRA2.19800101.A1.05x0625.NA.nc4|tail -2
ncdump: MERRA2.19800101.A1.05x0625.NA.nc4: MERRA2.19800101.A1.05x0625.NA.nc4: NetCDF: HDF error


v4 mount test - mount -t nfs -o vers=4  192.168.1.225:/nfs /tmp/test/

ncdump  -h -s MERRA2.19800101.A1.05x0625.NA.nc4|tail -2
		:_Format = "netCDF-4" ;
}

It works fine.


>From 18.04 nfs server -

v3 mount test -

ncdump  -h -s MERRA2.19800101.A1.05x0625.NA.nc4 |tail -2
		:_Format = "netCDF-4" ;
}


      Works fine as expected. So something has changed between 18.04 and 20.04 that breaks v3 mounts it seems. Thanks.

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https://bugs.launchpad.net/bugs/1903974

Title:
  issue reading netcdf4 files with nfs v3 on ubuntu 20.04

Status in nfs-utils package in Ubuntu:
  New

Bug description:
  I was upgrading a small 16.04 hpc cluster to 20.04 and noticed the
  following. An nfs v3 mount causes netcdf4 file reads to fail. Nfs v4
  mounts from the nfs server running 20.04 works fine. Netcdf3 files
  work fine with both nfs v3 and v4 mounts. I checked a 16.04 setup and
  18.04 setup and they have no issues reading netcdf4 files with nfs v3
  mounts.

       To reproduce this issue, please try any netcdf4 file and try to read the headers like this - 
  ncdump -s -h <filename.nc>. I needed v3 mounts, as I am using posix acls with zfs on the nfs server. So this is an issue particular to nfs server on 20.04 and I would have to move to 18.04 and stay there for a lots of other 16.04 servers and clusters till a solution is found to this issue. Thanks.

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