[DRBD-user] throughput test goes faster on DRBD device than on low level device

Bart Coninckx bart.coninckx at telenet.be
Wed May 26 19:24:44 CEST 2010

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


Hi all,

used this benchmark script from the DRBD manual to test one resource:

TEST_RESOURCE=test
TEST_DEVICE=$(drbdadm sh-dev $TEST_RESOURCE)
TEST_LL_DEVICE=$(drbdadm sh-ll-dev $TEST_RESOURCE)
drbdadm primary $TEST_RESOURCE
for i in $(seq 5); do
  dd if=/dev/zero of=$TEST_DEVICE bs=512M count=1 oflag=direct
done
drbdadm down $TEST_RESOURCE
for i in $(seq 5); do
  dd if=/dev/zero of=$TEST_LL_DEVICE bs=512M count=1 oflag=direct
done

results were better for the DRBD device than for the low level device:

1+0 records in
1+0 records out
536870912 bytes (537 MB) copied, 2.04583 seconds, 262 MB/s
1+0 records in
1+0 records out
536870912 bytes (537 MB) copied, 2.25206 seconds, 238 MB/s
1+0 records in
1+0 records out
536870912 bytes (537 MB) copied, 2.7367 seconds, 196 MB/s
1+0 records in
1+0 records out
536870912 bytes (537 MB) copied, 2.67956 seconds, 200 MB/s
1+0 records in
1+0 records out
536870912 bytes (537 MB) copied, 2.67137 seconds, 201 MB/s
1+0 records in
1+0 records out
536870912 bytes (537 MB) copied, 2.76239 seconds, 194 MB/s
1+0 records in
1+0 records out
536870912 bytes (537 MB) copied, 2.72964 seconds, 197 MB/s
1+0 records in
1+0 records out
536870912 bytes (537 MB) copied, 2.7846 seconds, 193 MB/s
1+0 records in
1+0 records out
536870912 bytes (537 MB) copied, 2.77892 seconds, 193 MB/s
1+0 records in
1+0 records out
536870912 bytes (537 MB) copied, 2.75706 seconds, 195 MB/s

(first five compared to the last five)


How is this possible? I guess I shouldn't complain, but still ...

Thx!


Bart



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