All- I recently replaced our director with a newer system (newer hardware, newer OS & kernel, newer ipvsadm) and although nearly everything is functioning very well, since the start of the fall semester we've had some complaints about slow file uploads to our Blackboard learning management system (LMS). Normally I would immediately assume the problem is Blackboard (because it always is), but this time it looks like the issue may at least relate to the load balancer.
Our director: Hardware: Intel S5500 motherboard, dual Intel Xeon E5540 @ 2.53 GHz (hyperthreading is enabled), 8 GiB RAM, onboard Intel Gigabit NIC OS: RHEL 6.3, x86_64 Kernel: RHEL's 2.6.32-279.2.1 ipvsadm: 1.25-9.el6 (from EPEL) The director fronts several services (LDAP, smtp, unrelated http and https), but with respect to Blackboard, we're load balancing both http (which is little used) and https: $sudo ipvsadm -L -t bb.ndsu.nodak.edu:http Prot LocalAddress:Port Scheduler Flags -> RemoteAddress:Port Forward Weight ActiveConn InActConn TCP bb.ndsu.NoDak.edu:http wlc persistent 10860 -> blkbrd-app1.ndsu.NoDak.edu:h Route 1 0 3 -> blkbrd-app2.ndsu.NoDak.edu:h Route 1 0 0 -> blkbrd-app3.ndsu.NoDak.edu:h Route 1 0 0 $ sudo ipvsadm -L -t bb.ndsu.nodak.edu:https Prot LocalAddress:Port Scheduler Flags -> RemoteAddress:Port Forward Weight ActiveConn InActConn TCP bb.ndsu.NoDak.edu:https wlc persistent 10860 -> blkbrd-app1.ndsu.NoDak.edu:h Route 1 98 910 -> blkbrd-app2.ndsu.NoDak.edu:h Route 1 97 580 -> blkbrd-app3.ndsu.NoDak.edu:h Route 1 90 550 We are using DR and the real servers are correctly configured to avoid the ARP problem. This isn't our first rodeo; we've been using ipvs for more than a decade, though I will say that it's been so trouble-free for us that it's certainly possible I've forgotten something when setting up our recent refresh of the director. We're not having any complaints from users about file *downloads*, where the return traffic would of course be direct because of DR, but our instructors have been complaining that file uploads are quite slow. Obviously with uploads, a much larger percentage of the traffic goes through the director. Our blackboard admin has done repeated timings uploading a 624 MB file (a RHEL CD ISO) to Blackboard, first by uploading through the https virtual service on the director, and then by doing the upload by connecting directly to the each of the real servers, avoiding the vip. When he uploads directly to a realserver, it takes about 80-90 seconds to upload the ISO, so about as close to line rate as we can expect for the 100 MB connection from his workstation. When he uploads through the director, it reliably takes 4 minutes to 4 minutes 30 seconds. It's essentially taking three times as long to do the upload through the director as it is to do it directly. We're not seeing any errors or collisions on the director's NIC. Our network folks have also looked at the switch port and report no problems. The NIC has autonegotiated at 1 Gigabit full-duplex with the switch. Our network staff also indicate that even the largest traffic spike they've seen on the director's port is only about 24 MiB. At this point I'm thinking it likely has to be some TCP tuning that needs to be done, but I'm a little hesitant to just tune for large file transfers because the majority of the other services fronted by the director don't need that. Can anyone provide some suggestions for things to look at or tunables I should consider? Any thoughts appreciated! Tim -- Tim Mooney [email protected] Enterprise Computing & Infrastructure 701-231-1076 (Voice) Room 242-J6, IACC Building 701-231-8541 (Fax) North Dakota State University, Fargo, ND 58105-5164 _______________________________________________ Please read the documentation before posting - it's available at: http://www.linuxvirtualserver.org/ LinuxVirtualServer.org mailing list - [email protected] Send requests to [email protected] or go to http://lists.graemef.net/mailman/listinfo/lvs-users
