[kwlug-disc] Accessing recently-written NFS files

[Paul Nijjar]

I do not have direct experience with this. I was going to suggest
enabling logging with the "rpcdebug" command, but maybe that command
has been deprecated? It does not seem to exist on Debian any more.

While I was trying to look up rpcdebug I ran into (what else?) the
ArchLinux wiki:
https://wiki.archlinux.org/title/NFS/Troubleshooting#Close-to-open/flush-on-close

But do not think that 10 byte vs 10k files would be the difference
here? Do you get permission denied errors if you run the below loop
with 10 byte files, but run it 10000 times? Still, this seems like it
might be worth investigating if you haven't done so already. 

Windows also comes with its own logs, which can sometimes be helpful.
If the FS is being served by a Windows machine is it serving as the
NFS server, and RH7 is the client? You can look in Event Viewer for
logs on the Windows side:
https://techcommunity.microsoft.com/t5/storage-at-microsoft/server-for-nfs-diagnostics/ba-p/424632

(Apologies if this is something you have already investigated. I am
aware you are also capable of using a search engine.)

- Paul

On Mon, Dec 12, 2022 at 05:45:04PM -0500, Adam Glauser wrote:
> I've got a bit of a head-scratcher on my hands.
> 
> I have a filesystem on my application's host (Oracle/RH Linux 7) that is
> mounted via NFS. I believe the FS is served by a Windows machine.
> 
> If I do something like this, everything is fine
> $ for i in {1..100};
> do
> head -c 10 </dev/urandom >"/nfs_share/tmp/test_file${i}";
> done && find /nfs_share/tmp/ -name test_file* -exec mv {}
> /nfs_share/final_location
> \;
> 
> However, if I bump up the file size to 10K, suddenly they all fail to mv
> with "Permission denied" errors. Waiting some time and retrying the 'mv'
> causes it to complete successfully.
> 
> I think this means that there is some kind of client-side caching
> happening, so that the file appears to be written, while NFS is still
> working away on transferring it to the storage location. Trying to unlink
> the file before the cache is emptied is disallowed, presumably to avoid
> data loss.
> 
> Am I headed in the right direction by trying to delve into the details of
> NFS caching and file locking? Any other avenues that someone can suggest?
> 
> Thanks,
> Adam

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