Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
Hi, I'm setting up a DRBD system and I don't really understand the performance hits I'm getting. I have two hosts (with dedicated GB LAN): Host1: 3Ware 9650 SE SATA2 hardware RAID6, 5x 2TB disks Host2: 2x250GB Linux MD RAID1. Example: a fully synced DRBD device with ext3 on it, writing a file with dd. Writing on host1: dd if=/dev/zero of=groot1 bs=10M count=50 50+0 records in 50+0 records out 524288000 bytes (524 MB) copied, 8.04722 s, 65.2 MB/s This is as expected, because the DRBD sync speed is 60 MB/s. When I make the device primary on host 2, it slows down: dd if=/dev/zero of=groot2 bs=10M count=50 50+0 records in 50+0 records out 524288000 bytes (524 MB) copied, 14.2884 s, 36.7 MB/s Why would it be slower when being primary on host2? I mean, writes have to be completed on both nodes anyway. And, even when I disconnect the device, the speed stays low on host2. When I do that on host1, speed rises far above that limit of 60 MB/s. Writing to another logical volume on the same MD RAID1 on host2 gives: dd if=/dev/zero of=/root/groot2 bs=10M count=50 50+0 records in 50+0 records out 524288000 bytes (524 MB) copied, 5.66666 s, 92.5 MB/s So, the server itself can handle high speeds just fine. Another thing I noticed, is that performance of the device is much slower when I use it as Xen DomU (virtual machine) storage then when I mount the block device directly. Performance is often merely 25 MB/s. Any insight is appreciated.