On Mon, 6 Nov 2006, David Severance wrote:
> The NFS solution
> Centralized storage (a NetApp in our case) which is shared via NFS to a
> pool of IMAP servers behind a Foundry ServerIron doing a nice job of
> load balancing users. Clients connect and are sent to whichever IMAP
> server is least busy and each server accesses files via NFS. The pluses
> for this approach are a robust storage system with alerts, double parity
> and enterprise quality. Shared IMAP servers so no user is ever down if a
> server breaks, the load balancer sends the user to another machine and
> we are alerted. The load balancer itself can also be configured to fail
> over to another load balancer (although the budget for that hasn't
> materialized yet). It's also easy to configure for end users who just
> use one FQDN to configure their software. The minuses for this approach
> are that we are stuck using mbox due to NFS lock issues and even then
> with limitations. We are happy to accept the only one client can access
[snip..]
Just be aware that it is not unusual for an IMAP client to open 2 (or
more) connections to a mail folder in the same session. It's pretty
common for a client to promptly open one connection to the INBOX so
to watch for new messages and have another that 'roams' around to
other mailboxes for fetching/storing messages. That 'roamer' may
return to the INBOX on occasion. With your load-balancer, you're
likely to have these various sessions end up on different IMAP servers
and thus see that cache-consistency problem that Mark keeps bringing
up. (unless that's a darned smart load-balancer which looks for
pre-existing sessions and tries to keep them together).
--
Dave Funk University of Iowa
<dbfunk (at) engineering.uiowa.edu> College of Engineering
319/335-5751 FAX: 319/384-0549 1256 Seamans Center
Sys_admin/Postmaster/cell_admin Iowa City, IA 52242-1527
#include <std_disclaimer.h>
Better is not better, 'standard' is better. B{
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