On 2021-08-05 5:53 p.m., Janusz
Jaskiewicz wrote:
Hello.
I'm experimenting a bit with DRBD in a cluster managed by Pacemaker.
It's a two node, active-passive cluster and the service that I'm trying to put in the cluster writes to the file system.
The service manages many files, it appends to some of them and increments the single integer value in others.
I'm observing surprising behaviour and I would like to ask you if what I see is expected or not (I think not).
I'm using protocol C, but still I see some delay in the files that are being replicated to the secondary server.
For the files that increment the integer I see a difference which corresponds roughly to 1 second of traffic.
I'm really surprised to see this, as protocol C should guarantee synchronous replication.
I'd rather expect some delay in processing (potentially slower disk writes due to the network replication).
The way I'm testing it:
The service runs on primary and writes to DRBD drive, secondary connected and "UpToDate".
I kill the service abruptly (kill -9) and then take down the network interface between primary and secondary (kill and ifdown commands in the script so executed quite promptly one after the other).
Then I mount the DRBD drive on both nodes and check the difference in the files with incrementing integer.
I would appreciate any help or pointers on how to fix this.
But first of all I would like to confirm that this behaviour is not expected.
Also if it is expected/allowed, how can I decrease the impact?
Please find below my configuration:
global_common.conf:
global {
usage-count yes;
udev-always-use-vnr; # treat implicit the same as explicit volumes
}
common {
handlers {}
startup {}
options {}
disk {}
net {
protocol C;
}
}
my_resource.conf:
resource wyr-dim-persistence {
on dimprod01.my.clustertest.com {
device /dev/drbd1;
disk /dev/mapper/drbdpool-drbdata;
address 192.168.0.1:7789;
meta-disk internal;
}
on dimprod02.my.clustertest.com {
device /dev/drbd1;
disk /dev/mapper/drbdpool-drbdata;
address 192.168.0.2:7789;
meta-disk internal;
}
}
What filesystem are you using? Is it cluster / multi-node aware?
-- Digimer Papers and Projects: https://alteeve.com/w/ "I am, somehow, less interested in the weight and convolutions of Einstein’s brain than in the near certainty that people of equal talent have lived and died in cotton fields and sweatshops." - Stephen Jay Gould
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