NFS write corruption on 8.0-RELEASE
olli at lurza.secnetix.de
Fri Feb 12 18:21:09 UTC 2010
Dmitry Marakasov wrote:
> * Oliver Fromme (olli at lurza.secnetix.de) wrote:
> > This is an excerpt from Solaris' mount_nfs(1M) manpage:
> > File systems that are mounted read-write or that con-
> > tain executable files should always be mounted with
> > the hard option. Applications using soft mounted file
> > systems may incur unexpected I/O errors, file corrup-
> > tion, and unexpected program core dumps. The soft
> > option is not recommended.
> > FreeBSD's manual page doesn't contain such a warning, but
> > maybe it should. (It contains a warning not to use "soft"
> > with NFSv4, though, for different reasons.)
> 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'm sorry for the confusion ... I do not think that it's
the cause for your data corruption, in this particular
case. I just mentioned the potential problems with "soft"
mounts because it could cause additional problems for you.
(And it's important to know anyhow.)
> 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, this is what happens if the network hangs:
1. With "hard" mounts (the default), processes that access
NFS shares are locked for as long as the network is down.
2. With "soft" mounts, binaries can coredump, and many
programs won't notice that write access just failed which
leads to file corruption.
Personally I definitely prefer the first.
Oliver Fromme, secnetix GmbH & Co. KG, Marktplatz 29, 85567 Grafing b. M.
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