One important question to be answered before you install the operating system is how you plan to protect your server(s) against disk failures. This means hardware failures as well as failures caused by an operating system or misusage of the system. You can, of course, try to ignore them and rely on you luck - but think again; how possible might be a disk failure and what impact does it have to my daily business and how much money do I have to spend to avoid them?

In modern operating environment, the need of protecting the systems against hardware failures is critical, and easier to implement than to trying to recover from a failure.

Nowadays the prices of additional hardware (disks and adapters) is reasonable even for smaller systems to implement mechanism to avoid and recover from disk failures. Furthermore modern operating systems offer the possibility to create software-based RAID (Redundant Array of Independent Disks) with minimal overhead associated to that task. Hardware RAID adapters are available which offers improved performance by offloading the task of creating and managing and disk array from the operating systems. And beyond that, some disk subsystems implement RAID capabilities which moves the RAID logic and administration completely away from the server side.

If you have a disk subsystem like the IBM FAStT, ESS or DS range then you control the RAID functions directly with the device controls. This disks subsystem then presents the disks to AIX and AIX is not aware that the disks are protected by the disks subsystem.

The alternative is a RAID via a RAID capable PCI adapter. Here you have this "catch 22" problem. How can you set this up before you install the operating system which could be AIX or Linux? Clearly you can't, for example, make the four disk into to a RAID5 set with the OS running as this involves a low level reformatting of the disks.

This is what to do:

1. If this machine is partitioned - create the LPAR (also works in the Full System Partition)
2. Boot from the Hardware Diagnostics CDROM.
3. Then find the Device Adapters section and the RAID setup menu.
4. Next, change the disks to RAID Candidate.
5. For RAID5, three disks are a minimum but four is much better and wastes less disk space.
6. Then create the RAID Array, where you can choose the level of RAID.
7. This will then format the disks for half an hour or more.
8. Once complete, exit the menus and restart the machine/LPAR but boot from the AIX/Linux installation from CDROM or the network
9. It will find one large disk (assuming RAID5?) instead of the smaller physical disks.

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