Hi Steve,After almost three months of production, with four mailstore servers, we see a pretty predictable 1,400-1,800 active sessions per mailstore, between 8:00 am and 9:00 pm. Of those, about 200-250 sessions per server are IMAP, which seems to map out to about 300-400 IMAP connections per server. And, I must admit, it always amazes me how low those numbers are. But, they do translate into between 130,000 and 140,000 LOGIN's per server, per day. Our IMAP connection counts are much lower than we originally expected. Despite that, I'm a lot less worried about the effect of IMAP clients than I used to be. Because Zimbra does support the IDLE command, and because most modern IMAP clients don't actively poll or hold as many connections as they can, I think the opinions expressed at the Zimbra class were -- umm ... not the opinions of someone intimately familiar with the nuances of large, modern IMAP deployments. *cough* If you ran a shop where, every night, 20,000 people turn off their computer, and then every morning at 8:00 am, 20,000 people turn their computer on and log into mail -- then I think you'd have a lot more cause for concern. If you're anything like we are, though, people tend to lock their screens and leave their computers on all night. And because of vagaries of traffic and class schedules, we see a much more progressive ramp-up in connections between 7:00 am and 9:00 am. I can say, though, we were initially very concerned about IMAP client connections, and got some pretty good help from Zimbra engineering to tune our deployment for about 2,500 connections per server. The Zimbra tuning guide says some pretty conservative things about IMAP tuning, but we were able to get some pretty high-level engineering assurances that, if we had that many connections, we'd be able to handle them. The short answer seems to be, "if you have enough memory, you can do it." Without a doubt, though, our bottleneck is disk throughput, not processors or memory. If you'd like, I'll try to say something more meaningful, later, but I've been dragging this message on for about 5 hours, and just need to hit send. I really think you'll be fine, though.
-- Tom Golson Senior Lead Systems Engineer Opensystems Group Computing & Information Services Texas A&M University Steve Hillman wrote:
Hi folks, We've been having discussions at our site about how best to step around the issue of supporting IMAP on Zimbra. Our current system (pre-Zimbra) supports IMAP, but we've traditionally been a POP site, and more recently a Webmail site (primarily for students). Our Webmail system uses POP, so it doesn't integrate with IMAP. But that all changes with Zimbra - it can provide much more seamless integration -- too seamless! Users will want to use it if they discover it. One of our developers was at Zimbra Admin training last month where it was pointed out that Zimbra doesn't scale that well for large numbers of IMAP users. So we're wondering what other sites are doing -- are you supporting much IMAP? (if so, how much, and are you seeing scaling issues?) If not, have you actually disabled it, actively discouraged it, or just not telling people about it?