mailbox files with "hole" on NFS, linux 2.6

[Eugene Crosser <crosser@rol.ru>]

I observe a problem that may be not Zmailer related, but maybe Matti or
somebody have any ideas.

I keep mailboxes on NFS for may years.  NFS server was perfiously Sorais
7, more recently Linux 2.6.x.  Clients are Linux boxes, shares are
mounted with nolock,nfsvers=3.  Clients where running 2.4x kernel for
years, with no problems.  In the past, I tried some early 2.6.x kernel
on the clients, and these days I installed 2.6.12.

On my past try to use 2.6 kernel I noticed a few cases of very
unpleasant data corruption, and apparently the same happend today.
Occationally a mailbox is noticed with big size, with a "home" in the
middle.  it starts as normal malbox, then there are lots of zeroes, and
before the end there is more normal mailbox data.  Apparently zeroes are
not real:

$ ls -l /var/virtual/online.ru/mail/F/U/uspvpr.broken
-rw-------  1 root root 13783233 Jun 21 21:32
/var/virtual/online.ru/mail/F/U/uspvpr.broken

$ du /var/virtual/online.ru/mail/F/U/uspvpr.broken
16      /var/virtual/online.ru/mail/F/U/uspvpr.broken

there is 16K of real data, the rest is a "hole".
I have TA_USE_MMAP=0 everywhere.
The problem happens rarely.  Still it looks rather bad.
The hole is observable on the nfs server machine as well as on clients.

Any ideas (other than rollback to 2.4, which I'll probably have to do if
no better solution is found)?

Eugene

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