Red Hat CLUSTER SUITE FOR ENTERPRISE LINUX 5.1 Instrukcja Użytkownika Pobierz pdf (Strona 19)

Introduction to Linux Clustering

best result, whereas others may find the performance of a SAN to be better.

Also consider future expandability – if you decide to grow the cluster in the future, a SAN

will probably be less expandable than a NAS. It's also easier to upgrade the speed of an

ethernet network with a faster switch, or more ethernet cards in the servers.

7.1.3 COMMODITY NETWORK FILE SHARE

Another option for centralised storage is the use of a commodity server with a large number

of hard drives using RAID.

This can be used in two different ways:

1. Using a block sharing software solution such as iSCSI, ATAoE or GNBD, to

effectively create a cheap NAS using standard computer components.

2. Running a network file system such as CIFS or NFS.

Advantages

● Cheap and simple. You can use standard computer off the shelf from a local store to

built this.

Disadvantage

● Does not provide full redundancy in the event of failure of components such as

motherboard or CPU. However, this can be off-set using something DRBD which is

covered further on.

● Usually less performance than a SAN or NAS, which is tuned to allow maximum IO.

● iSCSI software targets might not be supported by your Linux vendor and may suffer

performance issues.

Redundancy

This tends to be limited to hardware redundancy of server. Typically a server will only have

disk redundancy (and ethernet via use of bonded interfaces), although some more expensive

models offer PSU and even CPU redundancy.

Once solution that allows good redundancy is to run two identical servers with DRBD and

replicate the filesystems between the servers – effectively both servers will have exactly the

same data on them.

Ideal use

An iSCSI software target running on a server can provide a cheap NAS emulator for use in

development environments.

This solution could be used anywhere a NAS is, however it will require careful tuning and

smart hardware purchases to get optimal performance. One example that will make a

difference is where or not your ethernet cards have TCP off-load engines, which will

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Red Hat CLUSTER SUITE FOR ENTERPRISE LINUX 5.1 Instrukcja Użytkownika Strona 19