Re: zero bytes in files written to NFS

[Thomas Klausner <wiz%NetBSD.org@localhost>]

On Sat, Mar 27, 2021 at 12:22:35PM +0100, Thomas Klausner wrote:
> For a few months now (at least since November) I see broken files when
> writing from NetBSD-current/amd64 to a Synology (Linux) file server
> via NFS.  I don't have a completely reliable way to reproduce this,
> but it happens quite a lot when I run pkgsrc/archivers/torrentzip on
> large files (1-50GB) on file systems that are mounted via NFS. (The
> torrentzip tool reads the complete zip archive and replaces it with
> particular zlib settings and zip metadata.)
> 
> I thought it could be a problem with the NFS server, but I've replaced
> the server hardware, and it still happens.
> 
> I thought it could be a bug in the torrentzip tool, but it also
> happens (very rarely) when downloading files using filezilla (sftp)
> from a remote server directly to the NFS mounted device.
> 
> The breakage always looks the same way - a block of zero (NUL) bytes
> in the middle of the file. The amounts differ, but usually it's a
> couple of kB of zeroes.
> 
> So far I have not noticed this issue on local file systems.
> 
> So I assume it's a bug in NFS and/or UVM.
> 
> Has anyone else seen something similar?

I was asked offlist:

Yes, I see wcc errors like these:

Mar 29 20:51:20 yt /netbsd: [ 208996.0919434] 192.168.0.18:/volume2/foo: re-enabling wcc
Mar 29 20:51:20 yt /netbsd: [ 209116.2535171] 192.168.0.18:/volume2/foo: inaccurate wcc data (ctime) detected, disabling wcc (ctime 1617042615.889440844 1617042615.889440844, mtime 1617042615.889440844 1617042615.889440844)

Perhaps that's the root issue?
 Thomas