Novell LINUX ENTERPRISE 11 - HIGH AVAILABILITY, Руководство пользователя, Страница: 131 / 298

14
Distributed Replicated Block
Device (DRBD)
DRBD allows you to create a mirror of two block devices that are located at two different
sites across an IP network. When used with OpenAIS, DRBD supports distributed high-
availability Linux clusters.
IMPORTANT
The data traffic between mirrors is not encrypted. For secure data exchange,
you should deploy a virtual private network (VPN) solution for the connection.
Data on the primary device is replicated to the secondary device in a way that ensures
that both copies of the data remain identical. When using a cluster aware file system
such as ocfs2, it is also possible to run both nodes as primary devices.
By default, DRBD uses the TCP port 7788 for communications between DRBD nodes.
Make sure that your firewall does not prevent communication on this port.
You must set up the DRBD devices before creating file systems on them. Everything
pertaining to user data should be done solely via the
/dev/drbd<n>
device and not
on the raw device, as DRBD uses the last 128 MB of the raw device for metadata. Make
sure to create file systems only on the
/dev/drbd<n>
device and not on the raw de-
vice.
For example, if the raw device is 1024 MB in size, the DRBD device has only 896 MB
available for data, with 128 MB hidden and reserved for the metadata. Any attempt to
access the space between 896 MB and 1024 MB fails because it is not available for
user data.
Distributed Replicated Block Device (DRBD) 121