Datasheet

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members of the cluster to ﬁnd out which nodes in the cluster are active.

If a node fails, it does not emit a signal. In this case, heartbeat ensures

that another node takes over the relevant tasks and identity and makes the

failover known within the network. This means that the cluster remains

consistent. At present, the heartbeat failover function is limited to two

nodes.

19.4.2 RAID

RAID (redundant array of independent disks) brings together several hard

disk partitions to form a large virtual hard disk. RAID can be used to opti-

mize the performance and data security of your system. RAID levels 1 and

5 offer protection against the failure of a disk because the data is recorded

on several disks at the same time. This ensures that the complete data

record is always available on another disk in the system should a disk fail.

Find more information about RAID with SUSE LINUX in Section 3.11 on

page 145.

19.4.3 rsync

rsync can be used to synchronize large amounts of data between a server

and its backup. rsync has sophisticated mechanisms for only transferring

changes to ﬁles. This applies not only to text ﬁles, but also to binary ﬁles.

To enable the differences between ﬁles to be identiﬁed, rsync divides the

ﬁles into blocks and calculates checksums for these blocks. Find more infor-

mation about rsync in Section 23.6 on page 569.

19.4.4 DRBD

Distributed replicated block device (drbd) mirrors (RAID1) partitions and log-

ical volumes (data areas) by means of a normal network on the basis of

TCP/IP. Each node has a particular drbd resource active and all changes

are mirrored as secure transactions.

drbd has additional features in comparison with RAID1 for local disks that

enable the resynchronization time to be minimized after the two nodes

have been disconnected brieﬂy and a robust check after various malfunc-

tions to establish which side has the latest, consistent data.

398 19.4. The Software Side of High Availability