Red Hat CLUSTER SUITE FOR ENTERPRISE LINUX 5.1 Instrukcja Użytkownika Pobierz pdf (Strona 26)

Introduction to Linux Clustering

In the event of any node failing, Redhat

Cluster Suite will move all the services to

the alternate node and switch DRBD from

secondary to primary on the new master

node.

● A network failure runs the risk of a split-

brain situation – if neither node can see

the other, they will both try and become

master. To fix this, run ping to a remote

server to provide a tie-breaking third vote

(Quorum heuristics).

● If you have a SAN or NAS, instead of

storing the data locally and replicating

with DRBD, the attached storage device

could be used instead.

The SAN could be setup with a non-clustered or a clustered filesystem, the difference

being that a clustered filesystem is required if you require both servers to be able to

run services at once

If using a SAN, the cluster is scalable to more than two nodes, but the SAN could

become a single point of failure for the cluster and are a lot more expensive than

software solutions like DRBD.

Suitable Environments:

● Making any mission critical server HA.

● Any business or organisation that can not tolerate hardware downtime of their

production sever.

● Ecommerce servers that need to provide mail/websites/databases.

● Small hosting organisations. (larger ones should use designs like the one below)

8.2 Five node HA cluster with DRBD

One of the problems with DRBD is that it only works for two-node clusters. It is possible to

add a third node if the commercial version is purchased, but no DRBD solution exists which

can work more than three nodes at max.

When building clusters, it is more economical to have a single multi-node cluster rather than

many two-node clusters, as only one computer needs to be set aside for spare resources.

host2

host1

switch

floating IP

smart

power

switch

sda

DRBD

internet

remote host

for

quorum ping

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