Problem while deleting mailbox on a private spool on NFS

[Aleksandar Milivojevic]

Michael Loftis wrote:

> Don't use Cyrus over NFS.  It's not safe.  You *WILL* end up with 
> corrupt mailboxes.
> 
> There might be some NFS Client+Server combinations that are safe, but 
> since you've a Linux client I'm guessing your NFS server is also Linux, 
> a known not-safe configuration.  The reason is file locking doesn't' 
> really work on NFS.

Plus, couple of days ago I stumbled accross data corruption problem when 
file on NFS mounted partition is mmaped on Linux client (CentOS 4, which 
is RHEL 4 clone, kernel 2.6.9-5.0.3.EL).  Quick grep of Cyrus sources 
shows that Cyrus uses mmap in several places in the code, and I would 
guess DB libraries also make use of it.  So even if the file locking 
worked, there are more severe problems on Linux NFS clients.  This might 
or might not be connected with the problem OP experienced.  Basically, 
people running Cyrus over NFS on Centos4/RHEL4 (and probably other 
distros) should get a bit worried.

I found the problem when experimenting with one small app for creating 
nul-filled files that is good candidate for "the most stupid use of mmap 
that can trash your PC just like that".  Note that I haven't got 
confirmation that folks over at Red Hat were able to reproduce the 
problem.  I tested with single  NFS client and single NFS server, so 
there is probability that the problem is not general and exists only in 
specific configurations.  More info at:

https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=151284

-- 
Aleksandar Milivojevic <amilivojevic at pbl.ca>    Pollard Banknote Limited
Systems Administrator                           1499 Buffalo Place
Tel: (204) 474-2323 ext 276                     Winnipeg, MB  R3T 1L7
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