Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
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 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