To set up a DRBD primary node you need to configure the DRBD service, create the first DRBD block device and then create a file system on the device so that you can store files and data.
The DRBD configuration file /etc/drbd.conf
defines a number of parameters for your DRBD configuration,
including the frequency of updates and block sizes, security
information and the definition of the DRBD devices that you want
to create.
The key elements to configure are the on
sections which specify the configuration of each node.
To follow the configuration, the sequence below shows only the
changes from the default drbd.conf
file.
Configurations within the file can be both global or tied to
specific resource.
Set the synchronization rate between the two nodes. This is the rate at which devices are synchronized in the background after a disk failure, device replacement or during the initial setup. You should keep this in check compared to the speed of your network connection. Gigabit Ethernet can support up to 125 MB/second, 100Mbps Ethernet slightly less than a tenth of that (12MBps). If you are using a shared network connection, rather than a dedicated, then you should gauge accordingly.
To set the synchronization rate, edit the
rate
setting within the
syncer
block:
syncer { rate 10M; }
You may additionally want to set the
al-extents
parameter. The default for
this parameter is 257.
For more detailed information on synchronization, the effects of the synchronization rate and the effects on network performance, see Section 14.1.3.2, “Optimizing the Synchronization Rate”.
Set up some basic authentication. DRBD supports a simple password hash exchange mechanism. This helps to ensure that only those hosts with the same shared secret are able to join the DRBD node group.
cram-hmac-alg “sha1”;
shared-secret "shared-string
";
Now you must configure the host information. Remember that
you must have the node information for the primary and
secondary nodes in the drbd.conf
file
on each host. You need to configure the following
information for each node:
device
— the path of the
logical block device that will be created by DRBD.
disk
— the block device that
will be used to store the data.
address
— the IP address and
port number of the host that will hold this DRBD device.
meta-disk
— the location where
the metadata about the DRBD device will be stored. You
can set this to internal
and DRBD
will use the physical block device to store the
information, by recording the metadata within the last
sections of the disk. The exact size will depend on the
size of the logical block device you have created, but
it may involve up to 128MB.
A sample configuration for our primary server might look like this:
on drbd-one { device /dev/drbd0; disk /dev/hdd1; address 192.168.0.240:8888; meta-disk internal; }
The on
configuration block should be
repeated for the secondary node (and any further) nodes:
on drbd-two { device /dev/drbd0; disk /dev/hdd1; address 192.168.0.241:8888; meta-disk internal; }
The IP address of each on
block must
match the IP address of the corresponding host. Do not set
this value to the IP address of the corresponding primary or
secondary in each case.
Before starting the primary node, you should create the metadata for the devices:
root-shell> drbdadm create-md all
You are now ready to start DRBD:
root-shell> /etc/init.d/drbd start
DRBD should now start and initialize, creating the DRBD devices that you have configured.
DRBD creates a standard block device - to make it usable, you must create a file system on the block device just as you would with any standard disk partition. Before you can create the file system, you must mark the new device as the primary device (that is, where the data will be written and stored), and initialize the device. Because this is a destructive operation, you must specify the command line option to overwrite the raw data:
root-shell> drbdadm -- --overwrite-data-of-peer primary all
If you are using a version of DRBD 0.7.x or earlier, then you need to use a different command-line option:
root-shell> drbdadm -- --do-what-I-say primary all
Now create a file system using your chosen file system type:
root-shell> mkfs.ext3 /dev/drbd0
You can now mount the file system and if necessary copy files to the mount point:
root-shell> mkdir /mnt/drbd root-shell> mount /dev/drbd0 /mnt/drbd root-shell> echo "DRBD Device" >/mnt/drbd/samplefile
Your primary node is now ready to use. You should now configure your secondary node or nodes.
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