File Locking

[phil]

I've been doing some research on file locking for mail systems and have noticed in several places mention made to IMAP "[Not needing file locking]".   In doing a search on the UW /imap site all I can find is a reference to implications of locking with c-client.   If I understand correctly c-client is a library that aides in development of email systems. Is this library used in general distributions of the UW Imap server? I guess what I'm asking is does the information listed regarding c-client have any impact on an installation of IMAP as already developed and distributed, or is it a concern for those developing additional software?   Here is why I'm concerned about file locking. Consider a system that has one or several IMAP Servers, three or more sendmail servers and at least one pop server that must all access the same data server. This data server contains mailboxes for customers that either access their email over webmail or through outlook express. Because of the nature of this distributed architecture the current chosen solutions for data mounts are either NFS or Lustre Lite.   NFS is notorious for file locking problems, but in our initial benchmarks seems to actually perform faster than Lustre on simultaneous processes to multiple files. The determining factor would be then this: do the services requiring access to the data allow use of system file-locking mechanisms, or must they all use a lock file. My research on how IMAP handles file locking is ambiguous, but my case is this: IMAP must now how to retrieve the data while sendmail is simultaneously writing to the file, or requesting to write to a file. POP must also know when these  "locks" are in place. If IMAP must create a file to accomplish this Lustre will perform no better than NFS because Lustre only makes improvements on the way locks are placed as requested by the calling system.   As a final note, 1) I realize everyone says "do not implement email over NFS" but that is currently the only alternative I can think of and 2)I know this must sound very green, but any help this list can render would be appreciated.    _   °v°  There's no place like root#cd ~/  /(_)\   ^ ^