[DRBD-user] Secondary server works harder than primary

Gouveia, Chris Chris.Gouveia at spirent.com
Wed Jun 8 02:06:57 CEST 2011

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

I have a two machine DRBD setup, supposedly with identical hardware in
both machines. I have 3 drives in each, with software RAID-0, and DRBD
on the RAID partition. When I write large amounts of data via NFS to the
DRBD partition, the harddrive LED on the primary machine blinks slowly.
However, on the secondary machine, the LED is on solidly. I also ran
iostat on the drives:

Primary machine
avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           0.25    0.00    4.93   25.52    0.00   69.30

Device:            tps   Blk_read/s   Blk_wrtn/s   Blk_read   Blk_wrtn
sda             349.00     34960.00       680.00      34960        680
sdb             330.00     35112.00       544.00      35112        544
sdc               6.00         0.00       144.00          0        144
md0            2517.00    105736.00      1920.00     105736       1920

Secondary machine
avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           0.00    0.00    2.51    0.00    0.00   97.49

Device:            tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn
sda             937.00         0.00     16316.00          0      16316
sdb             986.00         0.00     16248.00          0      16248
sdc             905.00         0.00     16324.00          0      16324
md0           12116.00         0.00     48464.00          0      48464

Notice that the secondary machine TPS is much higher than the primary

The two machines have identical configurations:

resource hnlcsv {
	protocol	B;

	handlers {
/usr/lib/drbd/notify-emergency-reboot.sh; echo b > /proc/sysrq-trigger ;
reboot -f";
/usr/lib/drbd/notify-emergency-reboot.sh; echo b > /proc/sysrq-trigger ;
reboot -f";
		local-io-error	"/usr/lib/drbd/notify-io-error.sh;
/usr/lib/drbd/notify-emergency-shutdown.sh; echo o > /proc/sysrq-trigger
; halt -f";

	net {
		max-epoch-size	16000;
		max-buffers	16000;
		sndbuf-size	0;

	disk {

	syncer {
		al-extents	3389;
		rate 50M;

	on hnlcsv4 {
		device	/dev/drbd0;
		disk	/dev/md0;
		flexible-meta-disk	internal;

	on hnlcsv3 {
		device	/dev/drbd0;
		disk	/dev/md0;
		flexible-meta-disk	internal;

Does anyone know what could cause the secondary to work so hard? I think
if it didn't have to, I could get much higher throughput on my DRBD
partition because it's being limited by the secondary machine.

Chris Gouveia

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