[DRBD-user] Diagnosing DRBD Slowness

Robinson, Eric eric.robinson at psmnv.com
Tue Oct 21 22:06:56 CEST 2008

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

> Hm, how fast is 

> % dd if=/dev/zero of=/dev/null bs=1M count=100

[root at ha03 download]# dd if=/dev/zero of=/dev/null bs=1M count=100
100+0 records in
100+0 records out
104857600 bytes (105 MB) copied, 0.00234371 seconds, 44.7 GB/s

That looks pretty dang fast to me. 

However, I can eliminate the network link by piping it to nc running on
the same host, and guess what? Now it's slow again...

[root at ha03 download]# ifconfig eth3
eth3      Link encap:Ethernet  HWaddr 00:15:17:5C:1B:1B
          inet addr:  Bcast:  Mask:
          inet6 addr: fe80::215:17ff:fe5c:1b1b/64 Scope:Link
          RX packets:53291576 errors:0 dropped:0 overruns:0 frame:0
          TX packets:94847554 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:3761343430 (3.5 GiB)  TX bytes:4219210262 (3.9 GiB)
[root at ha03 download]#
[root at ha03 download]# nc -l 10000 &
[1] 19909
[root at ha03 download]# dd if=/dev/zero bs=1M count=100 | nc 10000
7+0 records in
6+0 records out
6291456 bytes (6.3 MB) copied, 19.1196 seconds, 329 kB/s

[root at ha03 download]#

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