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

[Lee Riemer]

Are the nodes identical hardware?  I assume you've got at least 2 
Gig-E's worth of bandwidth to the other node.

Is it replicating to the other node when you test the local device?

On 5/26/2010 12:24 PM, Bart Coninckx wrote:
> 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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