Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
Hi, Lars Ellenberg wrote: > On Mon, Feb 16, 2009 at 10:51:45AM +0000, Igor Neves wrote: > >> Hi, >> >> Some of you may know my problem since I have been discussing it with you >> in the IRC in the last few days, but I will explain it. >> >> I'm doing some tests with drbd with xen virtual machines, our solution >> was with vmware and drbd, but this solution it's with very low >> performance compared to xen, and i'm trying to improve our solution to xen. >> >> I started my tests with xen on both machines (node1 & node2). Both >> machines have 3 disks, sdb it's the drbd0. >> >> The disk can only deliver 102MB/sec writing, following seagate, and I >> get about 105MB/sec from each disk in direct access. >> I started my resouce in drbd and i'm able to sync at about 95MB/sec, >> which it's very good. Testing the disk with dd or with your benchmark >> tool called md, I get about 85MB/sec writing, which it's not bad. >> >> Now when I start the Xen Windows HVM Virtual Machine on node1 and I give >> "/dev/drbd0" as a block device, it works great, but inside windows VM, I >> get: >> - With drbd rpm package 8.2.6 from redhat and with this configuration >> "al-extents 1801" i get about 45MB/sec writing inside VM. >> - With drbd rpm 8.2.7 and 8.3.0 from linbit and with this configuration >> "al_extents 1801" i get about 4MB/sec writing inside VM. >> - With source 8.2.7 and 8.3.0 from linbit and with "al_extents 1801" i >> get again 4MB/sec writing inside VM. >> >> Now what I have found it's, all this tests were made with drbd in >> connected & updated state. In the middle of the test if I do in node2 >> "drbdadm disconnect resource" I get the state WForconnection and Update >> on node1 and in that moment I start getting 85MB/sec. >> >> So inside Xen Windows HVM Virtual Machine in and with drbd under it as a >> block device i get: >> - drbd 8.2.6 from redhat and drbd connected = 45MB/sec, with drbd >> disconnected = 85MB/sec >> - drbd 8.2.7 from linbit and drbd connected = 4MB/sec, with drbd >> disconnected = 85MB/sec >> - drbd 8.3.0 from linbit and drbd connected = 4MB/sec, with drbd >> disconnected = 85MB/sec >> > > in 8.2.7, we introduced a new method to ensure write ordering > guarantees, which now needs to be explicitly disabled > if you live on a "safe" device (battery backed write cache, > or no cache at all), where this hurts performance. > > so where you had "no-disk-flushes" in drbd.conf before, > you now need an additional "no-disk-barrier". > > if that does not help, or if you did not have "no-disk-flushes" before, > let me know, and I try to come up with something else. > Ok, I have added "no-disk-barrier" and now I get about 50MB/sec inside the VM. Outside the VM, in host, I get about 85MB/sec and with resource disconnected I get 85MB/sec. It's there something we can do to get this 25MB/sec difference? > >> I know you can ask, it's not Xen block device driver? >> - Yes it could, so i have added the other disk (exacly equal to the one >> in drbd resource and with the same throughput) with direct access and >> inside THE SAME windows virtual machine, I have 100MB/sec writing to the >> disk, so the Xen block device it's going good and it's working like a >> charm. Besides that Xen block device does not know "connected" and >> "disconnected" as I explained in the early example. >> >> I have done this tests all again in node2 as Brian suggested, but i get >> exactly the same values in the tests. >> >> So there is a problem here with drbd<->xen, something I have not managed >> to find and could be a bug or maybe some bad configuration from my side. >> >> Please, someone with more experience help out on this. >> >> My kernel version it's "2.6.18-92.1.22.el5xen" and I'm with Centos 5 and >> with all the latest updates available. >> >> Thanks, >> Igor Neves >> Thanks, -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.linbit.com/pipermail/drbd-user/attachments/20090218/5d6bcfeb/attachment.htm>