[DRBD-user] slow write performance

rahulcs singh.rahul.1983 at gmail.com
Tue Sep 11 22:43:26 CEST 2012

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

I am using DRBD for syncing files between two machines on a LAN. I have
created a device on a file using dd if=/dev/zero of=/opt/drbd-test.loop
bs=1M count=200
losetup /dev/loop1 /opt/drbd-test.loop.

My drbd resource settings are as follows:
root at obelix101:/tmp# drbdsetup 1 show
disk {
        size                    0s _is_default; # bytes
        on-io-error             pass_on _is_default;
        fencing                 dont-care _is_default;
        max-bio-bvecs           0 _is_default;
net {
        timeout                 60 _is_default; # 1/10 seconds
        max-epoch-size          8000;
        max-buffers             8000;
        unplug-watermark        16;
        connect-int             10 _is_default; # seconds
        ping-int                10 _is_default; # seconds
        sndbuf-size             0 _is_default; # bytes
        rcvbuf-size             0 _is_default; # bytes
        ko-count                0 _is_default;
        after-sb-0pri           disconnect _is_default;
        after-sb-1pri           disconnect _is_default;
        after-sb-2pri           disconnect _is_default;
        rr-conflict             disconnect _is_default;
        ping-timeout            5 _is_default; # 1/10 seconds
        on-congestion           block _is_default;
        congestion-fill         0s _is_default; # byte
        congestion-extents      127 _is_default;
syncer {
        rate                    1024000k; # bytes/second
        after                   -1 _is_default;
        al-extents              3389;
        on-no-data-accessible   io-error _is_default;
        c-plan-ahead            0 _is_default; # 1/10 seconds
        c-delay-target          10 _is_default; # 1/10 seconds
        c-fill-target           0s _is_default; # bytes
        c-max-rate              102400k _is_default; # bytes/second
        c-min-rate              4096k _is_default; # bytes/second
protocol C;
_this_host {
        device                  minor 1;
        disk                    "/dev/loop1";
        meta-disk               internal;
        address                 ipv4;
_remote_host {
        address                 ipv4;

I am getting really bad write performance:

root at obelix101:/tmp# time dd if=/dev/zero of=/mnt/mysql/syncing_drbd bs=1M
12+0 records in
12+0 records out
12582912 bytes (13 MB) copied, 0.0686793 s, 183 MB/s

real    3m49.773s
user    0m0.000s
sys     0m0.168s

What am i doing wrong ?

Thanking you,
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