[DRBD-user] slow write performance

Dan Barker dbarker at visioncomm.net
Wed Sep 12 15:42:47 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.

a) use oflag=direct or dd will just test caching.
b) You show a 183MB/s rate, which is pretty good. However, the target
appears not to be the drbd volume, you don't say if the resource is
connected or waiting for connection, and you don't describe the underlying
c) How is /mnt/mysql/syncing_drbd related to opt/drbd-test.loop or

Dan (the top poster)

-----Original Message-----
From: drbd-user-bounces at lists.linbit.com
[mailto:drbd-user-bounces at lists.linbit.com] On Behalf Of rahulcs
Sent: Tuesday, September 11, 2012 4:43 PM
To: drbd-user at lists.linbit.com
Subject: [DRBD-user] slow write performance

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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