HOWTO: Multi Disk System Tuning

2. Structure

As this type of document is supposed to be as much for learning as a technical reference document I have rearranged the structure to this end. For the designer of a system it is more useful to have the information presented in terms of the goals of this exercise than from the point of view of the logical layer structure of the devices themselves. Nevertheless this document would not be complete without such a layer structure the computer field is so full of, so I will include it here as an introduction to how it works.

It is a long time since the mini in mini-HOWTO could be defended as proper but I am convinced that this document is as long as it needs to be in order to make the right design decisions, and not longer.

2.1 Logical structure

This is based on how each layer access each other, traditionally with the application on top and the physical layer on the bottom. It is quite useful to show the interrelationship between each of the layers used in controlling drives.

        ___________________________________________________________
        |__     File structure          ( /usr /tmp etc)        __|
        |__     File system             (ext2fs, vfat etc)      __|
        |__     Volume management       (AFS)                   __|
        |__     RAID, concatenation     (md)                    __|
        |__     Device driver           (SCSI, IDE etc)         __|
        |__     Controller              (chip, card)            __|
        |__     Connection              (cable, network)        __|
        |__     Drive                   (magnetic, optical etc) __|
        -----------------------------------------------------------

In the above diagram both volume management and RAID and concatenation are optional layers. The 3 lower layers are in hardware. All parts are discussed at length later on in this document.

2.2 Document structure

Most users start out with a given set of hardware and some plans on what they wish to achieve and how big the system should be. This is the point of view I will adopt in this document in presenting the material, starting out with hardware, continuing with design constraints before detailing the design strategy that I have found to work well. I have used this both for my own personal computer at home, a multi purpose server at work and found it worked quite well. In addition my Japanese co-worker in this project have applied the same strategy on a server in an academic setting with similar success.

Finally at the end I have detailed some configuration tables for use in your own design. If you have any comments regarding this or notes from your own design work I would like to hear from you so this document can be upgraded.

2.3 Reading plan

Although not the biggest HOWTO it is nevertheless rather big already and I have been requested to make a reading plan to make it possible to cut down on the volume

Expert

(aka the elite). If you are familiar with Linux as well as disk drive technologies you will find most of what you need in the appendices. Additionally you are recommended to read the FAQ and the Bits'n'pieces chapter.

Experienced

(aka Competent). If you are familiar with computers in general you can go straight to the chapters on technologies and continue from there on.

Newbie

(mostly harmless). You just have to read the whole thing. Sorry. In addition you are also recommended to read all the other disk related HOWTOs.