[DRBD-user] Very low write performance on local disks on XenServer 5.5 with DRBD

bugul at gmx.de bugul at gmx.de
Wed Mar 17 11:19:17 CET 2010

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


we use two Citrix XenServer 5.5 with DRBD and DRBD-Proxy and we have
very low write performance on local disks

Tests with bonnie++ in a Debian VM show these results:

(bonnie with drbd and primary/secondary uptodate)

Version  1.03       ------Sequential Output------ --Sequential Input-

                    -Per Chr- --Block-- -Rewrite- -Per Chr- --Block--

Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP
/sec %CP

test           512M 13325  22 12646   1   275   0 46463  34 129431   1
 2.4   0

                    ------Sequential Create------ --------Random

                    -Create-- --Read--- -Delete-- -Create-- --Read---

              files  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP
/sec %CP

                 16 +++++ +++ +++++ +++ +++++ +++ +++++ +++ +++++ +++
+++++ +++


The VM’s (Windows Server 2000) are very slow and hang sometimes.

Without DRBD we easily reach 100 MB/s (rw).

Strangely while the HDDs on the primary are active only sometimes the
secondary HDDs are permanently in use and there is a lot of traffic on
the DRBD network.

We use an extra NIC for DRBD on both servers and the connection for DRBD
is a SDSL with 2MBit sym.

dom0 is configured to use 2048MB (parameter dom0_mem).

Any ideas what to look for? Any help is highly appreciated!

Here is our /etc/drbd.conf:

global { usage-count yes; }

common {

  protocol A;

  net {

    shared-secret "xenserver";

    after-sb-0pri discard-zero-changes;

    after-sb-1pri consensus;

    after-sb-2pri disconnect;

    ping-timeout 20;


  disk {

    max-bio-bvecs 1;


  startup {

    # leave this disabled for now

    become-primary-on bornheim;


  handlers {

    split-brain "/usr/lib/drbd/notify-split-brain.sh";


  syncer { rate 284k; }


resource drbd-sr {

  device /dev/drbd1;

  disk /dev/sda3;

  meta-disk internal;

  syncer {

    csums-alg md5;


  proxy {

    compression on;

    memlimit 1024M;


  on bornheim {


    proxy on bornheim {





  on koeln {


    proxy on koeln {






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