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 <[email protected]>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 > [email protected] > http://lists.linbit.com/mailman/listinfo/drbd-user > -- Dr. Michael Iverson Director of Information Technology Hatteras Printing
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