[DRBD-user] Writes are much too slow

eBoundHost: Artur artur at eboundhost.com
Thu Sep 25 01:10:15 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.

Hi All, 

Putting together a system to compete with netapp and bluearc. I say 90% of it can be done with drbd and supermicro + LVM + ext3. 

Problem: slow write when server1 and server2 are connected. 

Server profile: 
server1: dualcore, 2gb ram, 1x500gb with 10 gb drbd0 on /dev/sda6. ext3 formatted. 
server2: dualcore, 4gb ram, 1x500gb with 10 gb drbd0 on /dev/sda6. ext3 formatted. 

Network: 1 gigabit connections, server to server direct. 

OS: Centos5.2 x 64 

Config file: 
global { usage-count yes; } 
common { 
syncer { 
rate 50M; 
resource r0 { 
protocol C; 
disk { 
net { 
cram-hmac-alg sha1; 
shared-secret "Foofsfafsfdtory"; 
device /dev/drbd0; 
disk /dev/sda6; 
meta-disk internal; 

on server1 { 

on server2 { 

Here are my benchmarks: 
dd if=/dev/zero bs=4096 count=10000 oflag=dsync of=/data/file1 

DRBD Active and connected: 
40960000 bytes (41 MB) copied, 24.8387 seconds, 1.6 MB/s 

DRBD Active and NOT connected: 
40960000 bytes (41 MB) copied, 10.8259 seconds, 3.8 MB/s 

File system partition, NON DRBD, same disk: 
40960000 bytes (41 MB) copied, 10.3686 seconds, 4.0 MB/s 

These are very consistent and repeatable. 

DRBD: built from source 8.2.6. installed as a module. tried the rpms from yum, similar results. 

Output of /proc/drbd: 
version: 8.2.6 (api:88/proto:86-88) 
GIT-hash: 3e6982sdfsdfsdffs28c1bfdf7d647169eba7d2eb4 build by root at server2, 2008-09-24 13:00:25 
0: cs:WFConnection st:Primary/Unknown ds:UpToDate/DUnknown C r--- 
ns:10055268 nr:0 dw:1680584 dr:9775393 al:112 bm:598 lo:0 pe:0 ua:0 ap:0 oos:211180 

Both hard drives are the same speed, confirmed with the same test from above. 

I've recompiled network drivers, recompiled drbd from source, now thinking to recompile the kernel. 

Checked that network is clear with wireshark, no errors. I've adjusted the buffers and other settings in drbd.conf and nothing i seem to do makes any difference. 

Would welcome any ideas or suggestions. 

Best Regards, 

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