dovecot - Mar 2007 - Newbie NFS question

As is usually the case, I'm not sure enough of what the DC docs are 
referring to; there are some implicit info assumptions that I, the 
Newbie, miss...

Anyway, here is my situation

Dovecot is to run on one machine only, its index files are stored in on 
a separate, non-quotaed, not NFS filesystem.
INBOX and folder filesystems (all mbox format) are native to this 
machine and are NFS exported to three machines with root access.  NFS 
access can be NFS V2, or 3 or 4.
1) a user maintenance server that may add or delete users and their 
INBOXES/folders
2) a mailing list server that writes mailings email to the NFS mounted 
file system of user INBOXes
3) A user login machine where the users may access their INBOXes and folders
All machines are running vanilla IBM AIX; I have never known there to be 
corruption from NFS locking problems, and am not aware of any 
locking/caching parameters for AIX's NFS implementation.  All machines 
are running NTP synched to a common NTP master server

My questions:
1) Since my index files are stored in on a separate, non-quotaed, not 
NFS filesystem, can I correctly assume this means I can ignore the 
nmap_disable and lock_method parms?
2) The docs say:
> The easiest way to get better performance without caching problems is 
> to just make sure the user is always redirected to the same server. If 
> you can manage to do that, then it's safe to enable attribute caching.
The INBOXes and folders live on the mail server where
a) DC is going to run and
b) they are exported to the three other machine.
Does this mean that I don't have to mess with actimeo?
3) Pardon my ignorance....Is actimeo set on the NFS server as an 
attribute of exportation or on the NFS client on the imported FS...or both
4) Is there any reason related to data integrity or performance to 
prefer NFS V2 or 3 or 4?
5) Are there other questions I should ask of IBM about NFS client and 
Server daemon config

Thanks in advance...........

-- 
===Stewart Dean, Unix System Admin, Henderson Computer Resources 
Center of Bard College, Annandale-on-Hudson, New York  12504  
sdean at bard.edu  voice: 845-758-7475, fax: 845-758-7035

On Wed, 2007-03-14 at 15:52 -0400, Stewart Dean wrote:
> 1) Since my index files are stored in on a separate, non-quotaed, not 
> NFS filesystem, can I correctly assume this means I can ignore the 
> nmap_disable and lock_method parms?
Right.
> 2) The docs say:
> > The easiest way to get better performance without caching problems is 
> > to just make sure the user is always redirected to the same server. If
> > you can manage to do that, then it's safe to enable attribute
caching.
> The INBOXes and folders live on the mail server where
> a) DC is going to run and
> b) they are exported to the three other machine.
> Does this mean that I don't have to mess with actimeo?
So Dovecot runs in one server, but the mails are exported to 3 other
servers too? If the other servers are accessing the mails at the same
time as Dovecot, there can be problems if you don't set actimeo=0.
Although I guess the worst that can happen is some "Invalid cached mbox
offset" errors in log file which are transparently fixed.
> 3) Pardon my ignorance....Is actimeo set on the NFS server as an 
> attribute of exportation or on the NFS client on the imported FS...or both
It's a NFS client setting.
> 4) Is there any reason related to data integrity or performance to 
> prefer NFS V2 or 3 or 4?
I don't think you should use NFSv2, but I don't know if NFSv4 is much
better than NFSv3. Although I think its locking worked better at least.
I think NFSv4's caching rules were also somehow different, but I don't
know if they make actimeo=0 unnecessary.
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