NFS write corruption on 8.0-RELEASE

[Rick Macklem]

On Fri, 12 Feb 2010, Dmitry Marakasov wrote:

>
> Interesting, I'll try disabling it. However now I really wonder why
> is such dangerous option available (given it's the cause) at all,
> especially without a notice. Silent data corruption is possibly the
> worst thing to happen ever.
>

I doubt that the data corruption you are seeing would be because of
"soft". "soft" will cause various problems w.r.t. consistency, but in
the case of a write through the buffer cache, I think it will leave the
buffer dirty and eventually it will get another write attempt.

> However, without soft option NFS would be a strange thing to use -
> network problems is kinda inevitable thing, and having all processes
> locked in a unkillable state (with hard mounts) when it dies is not
> fun. Or am I wrong?
>

Well, using NFS over an unreliable network is going to cause
grief sooner or later. The problem is that POSIX apps. don't
expect I/O system calls to fail with EIO and generally don't
handle that gracefully. For the future, I think "umount -F"
(a forced dismount that accepts data loss) is the best compromise,
since at least then a sysadmin knows that data corruption could
have occurred when they do it and can choose to "wait" until
the network is fixed as an alternative to the corruption?

rick