[CentOS] DRBD very slow....

Wed Jul 22 09:16:04 UTC 2009
Coert Waagmeester <lgroups at waagmeester.co.za>

Hello all,

we have a new setup with xen on centos5.3

I run drbd from lvm volumes to mirror data between the two servers.

both servers are 1U nec rack mounts with 8GB RAM, 2x mirrored 1TB
seagate satas.

The one is a dual core xeon, and the other a quad-core xeon.

I have a gigabit crossover link between the two with an MTU of 9000 on
each end.

I currently have 6 drbds mirroring across that link.

The highest speed I can get through that link with drbd is 11 MB/sec

But if I copy a 1 gig file over that link I get 110 MB/sec.

Why is DRBD so slow? 

I am not using drbd encryption because of the back to back link.
Here is a part of my drbd config:

# cat /etc/drbd.conf
global {
  usage-count yes;
common {
  protocol C;
  syncer { rate 80M; }
  net {
resource xenotrs {
  device    /dev/drbd6;
  disk      /dev/vg0/xenotrs;
  meta-disk internal;

  on baldur.somedomain.local {
  on thor.somedomain.local {

Kind regards,