[DRBD-user] drbd write performance slow, per disk 40M/s by dd command

[zf5984599]

hi，Felix, many thanks. 

I used this cmd, here is my result:
machine 1：
resource r0 {
    options {
    }
    net {
        max-epoch-size          20000;
        max-buffers             80000;
        sndbuf-size             1048576; # bytes
    }
    _remote_host {
        address                 ipv4 192.168.100.231:7788;
    }
    _this_host {
        address                 ipv4 192.168.100.213:7788;
        volume 0 {
            device                      minor 0;
            disk                        "/dev/sdd1";
            meta-disk                   internal;
            disk {
                al-extents              3389;
            }
        }
    }
}

machine 2：
resource r0 {
    options {
    }
    net {
        max-epoch-size          20000;
        max-buffers             80000;
        sndbuf-size             1048576; # bytes
    }
    _remote_host {
        address                 ipv4 192.168.100.213:7788;
    }
    _this_host {
        address                 ipv4 192.168.100.231:7788;
        volume 0 {
            device                      minor 0;
            disk                        "/dev/sdc1";
            meta-disk                   internal;
            disk {
                al-extents              3389;
            }
        }
    }
}

and when I retest, the results of 3 sequential tests are:

# dd if=/dev/zero of=test3 bs=1M count=800 conv=fdatasync
800+0 records in
800+0 records out
838860800 bytes (839 MB) copied, 24.6033 seconds, 34.1 MB/s

# dd if=/dev/zero of=test3 bs=1M count=800 conv=fdatasync
800+0 records in
800+0 records out
838860800 bytes (839 MB) copied, 22.9287 seconds, 36.6 MB/s

# dd if=/dev/zero of=test3 bs=1M count=800 conv=fdatasync
800+0 records in
800+0 records out
838860800 bytes (839 MB) copied, 10.151 seconds, 82.6 MB/s

So, the first and second times write-performance is so slow, 
but the 3rd performance is better ? what problem may induced this,
is my test method incorrect?

BRs,
feng









From: Felix Frank
Date: 2012-04-30 22:38
To: zf5984599
CC: drbd-user
Subject: Re: [DRBD-user] drbd write performance slow, per disk 40M/s by dd command
Hi,

On 04/26/2012 03:24 AM, zf5984599 wrote:
> I had turned off disk-barrier and disk-flushes in config file, but there
> is no difference.

did you make sure your tunings were applied correctly?
It's advisable to check using "drbdsetup 0 show" (if 0 is indeed the
minor number of the resource under test).

Your 100MBps result looks suspicious to me. Hum.

HTH,
Felix
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