On Thu, Jun 26, 2014 at 03:58:40PM +0000, robin.wakefi...@ubs.com wrote:
> We have been asked to consider using a set of 6 Postfix servers
> to provide a buffer between Exchange and our Compliance Archive
> servers,
Have seen this done before, Postfix queue between Exchange and downstream
archive.
> Normally Exchange will route directly to the archive servers,
> but can route via Postfix if required.
My experience is with a configuration that always queues to Postfix.
The Postfix queue in the middle used suitably HA SAN storage, which
was designed to avoid loss of data should a single server chassis
fail.
> If all the archive servers are down for a number of days, then the
> Postfix server will buffer the mails from Exchange.
Why not always send via Postfix? That way you know it works when you
need it. Postfix tries to deliver via the archive when the archive
is up, otherwise queues. If the archive is down for some time, you
can place new and old mail on "hold" until you administratively
re-enable delivery.
> This could potentially equate to 1-2 million messages being stored on
> each Postfix server.
That's fine. If you want the mail held, and not delivered, just
set a hash queue depth of 2, set "in_flow_delay = 0" and place all
incoming mail on hold.
> What are the pitfalls/recommendations for running Postfix against
> a large queue of 1 million messages?
Depending on the file-system, you may need to set a hash depth of
2 or more, and add "incoming, hold" to "hash_queue_names", giving:
hash_queue_depth = 2
hash_queue_names = deferred, defer, hold, incoming
> I was considering having a number of hold queues configured, with
> scripts to switch hold queues every hour.
No need.
> A second set of scripts would then release the held messages once the
> archive servers are back up. Is this
> required/recommended, or can Postfix cope with large queues on its
> own? Any other good ideas/experience doing this?
A large hold-queue is fine, provided your file-system can deal with
a couple of thousand messages per directory. Some file-systems
use hashed directories, that scale just fine.
--
Viktor.
