Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
With your setup, Your read performance is going to be limited by your RAID selection. Be prepared to experiment and document the performance of various different nodes. With a 1G interconnect, write performance will be dictated by network speed. You'll want jumbo frames at a minimum, and might have to mess with buffer sizes. Keep in mind that latency is just as important as throughput. There is a performance tuning page on the linbit site. I spent a day messing with various parameters, but found no appreciable improvements. With 4 drives, I think you'll get better performance with raid 10. However, I think you'll need to install a benchmark like iozone, and spend a lot of time doing before/after comparisons. Mike On Sat, Jun 5, 2010 at 10:27 AM, Miles Fidelman <mfidelman at meetinghouse.net>wrote: > Hi Folks, > > I've been doing some experimenting to see how far I can push some old > hardware into a virtualized environment - partially to see how much use I > can get out of the hardware, and partially to learn more about the behavior > of, and interactions between, software RAID, LVM, DRBD, and Xen. > > What I'm finding is that it's really easy to get into a state where one of > my VMs is spending all of its time in i/o wait (95%+). Other times, > everything behaves fine. > > So... I'm curious about where the bottlenecks are. > > What I'm running: > - two machines, 4 disk drives each, two 1G ethernet ports (1 each to the > outside world, 1 each as a cross-connect) > - each machine runs Xen 3 on top of Debian Lenny (the basic install) > - very basic Dom0s - just running the hypervisor and i/o (including disk > management) > ---- software RAID6 (md) > ---- LVM > ---- DRBD > ---- heartbeat to provide some failure migration > - each Xen VM uses 2 DRBD volumes - one for root, one for swap > - one of the VMs has a third volume, used for backup copies of files > > What I'd like to dig into: > - Dom0 plus one DomU running on each box > - only one of the DomUs is doing very much - and it's runnin about 90% > idle, the rest split between user cycles and wait cycles > - start a disk intensive job on the DomU (e.g., tar a bunch of files on the > root LV, put them on the backup LV) > - i/o WAIT goes through the roof > > It's pretty clear that this configuration generates a lot of complicated > disk activity. Since DRBD is at the top of the disk stack, I figure this > list is a good place to ask the question: > > Any suggestions on how to track down where the delays are creeping in, what > might be tunable, and any good references on these issues? > > Thanks very much, > > Miles Fidelman > > -- > In theory, there is no difference between theory and practice. > In<fnord> practice, there is. .... Yogi Berra > > > _______________________________________________ > drbd-user mailing list > drbd-user at lists.linbit.com > http://lists.linbit.com/mailman/listinfo/drbd-user > -- Dr. Michael Iverson Director of Information Technology Hatteras Printing -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.linbit.com/pipermail/drbd-user/attachments/20100605/47377656/attachment.htm>