Red Hat CLUSTER SUITE FOR ENTERPRISE LINUX 5.1 Instrukcja Użytkownika Pobierz pdf (Strona 17)

Introduction to Linux Clustering

Centralised storage systems typically export the disk space as a block device which appears

on the nodes as a local disk, which then needs to be partitioned and formatted – so you can

run whatever filesystem you wish on top of it.

This differers from network filesystems like NFS which appear as a mountable filesystems

and can not be partitioned or have other filesystems ontop of them.

7.1.1 SAN – STORAGE AREA NETWORK

A SAN is a hardware device consisting of a number of hard drives in RAID. The SAN is

then attached to each cluster node by fibre channel.

Advantages

● High-speed performance.

● Directly attached, so no issues due to network loss, congestion, etc.

● Tried and tested technology.

Disadvantages

● Expensive – every node needs to have a fibre channel communication card installed,

both the SAN and the fibre channel hardware is expensive.

● Limited scalability – the number of cluster nodes possible are limited by the number

of interfaces on the SAN.

Redundancy

For proper redundancy to prevent an outage in the

event of a hardware failure, it is required to

purchase two SANs which are capable of mirroring

each other, and having fibre channel cards in the

servers capable of talking to both SANs.

Without this redundancy all the work and resources

put into developing a high-availability cluster will

be wasted when the SAN dies.

Ideal Use

Suitable for use in clusters where all the nodes are located on the same physical site, as well

as being suitable for use in clusters requiring maximum I/O performance.

However for budget concious organisations, a NAS may be a better option.

host1 host2

SAN or NAS

Hot Spare

Replication

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Red Hat CLUSTER SUITE FOR ENTERPRISE LINUX 5.1 Instrukcja Użytkownika Strona 17