Setting up local synchronous replication using DRDB9

DRBD (Distributed Replicated Block Device) is a distributed, flexible and universally replicated storage solution for Linux.

DRBD has a superficial similarity to RAID-1 in that it includes a copy of the data on two storage devices so that in the event of a failure, the data on the other can be used. However, it works very differently than RAID and even network RAID.

In this article, I will share my experience on how to create drbd replication locally, not using drbdadm, but using drbdsetup and drbdmeta.

  • drbdadm: DRBD high level administration tool. It is used over drbdsetup and drbdmeta

  • drbdsetup: A lower-level administration tool for connecting DRBD devices to their backup devices, configuring pairs of DRBD devices to reflect their backup devices, and for checking the configuration of running DRBD devices.

  • drbdmeta: metadata management tool.

Test environment

Ubuntu 18.04, kernel version 4.19 and higher

Step 1. Installing and downloading the module

Vanilla kernels contain only the eighth version of DRBD, it is advisable to rebuild the kernels without this module, and install the ninth version from the repository.

Adding repositories to your sources.list

deb http://ppa.launchpad.net/linbit/linbit-drbd9-stack/ubuntu bionic main
deb-src http://ppa.launchpad.net/linbit/linbit-drbd9-stack/ubuntu bionic main

Update cache and install drbd packages

apt update
apt install drbd-dkms drbd-utils

Checking the module version and loading it with parameters

modinfo drbd
modprobe drbd usermode_helper=/bin/true minor_count=36

Step 2Setting up global_common.conf

I use the following config parameters, all the rest can be set when configuring the resource

# DRBD is the result of over a decade of development by LINBIT.
# In case you need professional services for DRBD or have
# feature requests visit http://www.linbit.com

global {
	usage-count no;
}

common {
	disk {
		c-delay-target 50;
		c-fill-target 0;
	}

	net {
		csums-alg hash-alg;
	}
}

You can read more about all the options here

Step 3Configure the DRBD9 Resource

What will be required:

  1. Two block devices (source and destination)

  2. Two logical volumes for metadata (I used 2 GB each)

Process of creation:

  1. Create two resources

drbdsetup new-resource drbdres0 0
drbdsetup new-resource drbdres1 1

where:

drbdres0 and drbdres1 – resource name

0 and 1 – peer node id

  1. Create drbd devices

drbdsetup new-minor drbdres0 0 0
drbdsetup new-minor drbdres1 1 0

where:

drbdres0 and drbdres1 – resources created earlier

the second argument (minor) is the number of the created device, i.e. drbd0, drbd1

the third argument is the volume number

  1. Creating metadata on volumes for metadata

drbdmeta --force 0 v09 '/dev/zd0' flex-external create-md 1
drbdmeta --force 1 v09 '/dev/zd16' flex-external create-md 1
  1. Add disks to previously created drbd devices

drbdsetup attach 0 '/dev/zd32' '/dev/zd0' flexible --disk-flushes=no --disk-barrier=no --al-extents=3389
drbdsetup attach 1 '/dev/zd64' '/dev/zd16' flexible --disk-flushes=no --disk-barrier=no --al-extents=3389

where:

the first argument (0 and 1) is the number of the created device (minor)

‘/dev/zd32’ and ‘/dev/zd64’ – source and destination

‘/dev/zd0’ and ‘/dev/zd16’ are previously created volumes for metadata and then parameters follow

  1. We create new peers

drbdsetup new-peer drbdres0 1 --protocol=C --max-buffers=36K --max-epoch-size=36K --sndbuf-size=1024K --rcvbuf-size=2048K
drbdsetup new-peer drbdres1 0 --protocol=C --max-buffers=36K --max-epoch-size=36K --sndbuf-size=1024K --rcvbuf-size=2048K

where:

drbdres0 and drbdres1 – previously created resources

the second parameter (1 and 0) is the peer node id followed by the connection parameters

  1. Create connection endpoints

drbdsetup new-path drbdres0 1 127.0.0.1:7788 127.0.0.1:7789
drbdsetup new-path drbdres1 0 127.0.0.1:7789 127.0.0.1:7788

Note: If you want to create even more resources locally, you will need to use other ports. for example: 127.0.0.1:7790 127.0.0.1:7791 and so on

  1. Adding Options

drbdsetup peer-device-options drbdres1 0 0 --c-plan-ahead=0 --resync-rate=80M
drbdsetup peer-device-options drbdres0 1 0 --c-plan-ahead=0 --resync-rate=80M

resync-rate is the maximum sync rate. Keep in mind that if you set the speed to high, then drbd will use the entire resource of the disk or logical volume, and if some application is running on it, then it will not get access to the disk until the synchronization is completed.

  1. Making the role primary for the first resource

drbdsetup primary drbdres0 --force
  1. Making a connection

drbdsetup connect drbdres0 1
drbdsetup connect drbdres1 0

After the performed actions when displaying the status

drbdsetup status -v

synchronization should start, after the end of synchronization, both resources should have UpToDate. You can read more about statuses here in the “Theory” section. Official site with documentation. Further, it is necessary to use newly created devices drbd0 / drbd1 for work, depending on which primary.

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