Caption for the graphic goes here: This is a Green Ball.
StructureA quick overview on how all parts fit together in the overall
structure. An example from the Multi Disk HOWTO is used.
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.
Logical structuredisk!structure, I/O subsystem
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.
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.
Reading planAs you go beyond 50 pages or so there will be a lot of
text that experts and even the experienced do not need to read.
Keeping in mind that we wish to care for all kinds of people in
the Linux world we might have to make a reading plan. Again,
an example follows from the Multi Disk HOWTO.
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 chapter.
Experienced
(aka Competent). If you are familiar with computers in
general you can go straight to the chapters on
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.
Technologies(your index root)!technologiesIntroduction of technology for the newbie with a few
references to detailed works. Remember that not everyone has
Internet access so you have to explain in sufficient details so
even the newbie can get by.Implementation(your index root)!implementationNow your readers should have a sufficient knowledge of
what this is about and now we come to the hands on of implementing
your clever scheme.Maintenance(your index root)!maintenanceFew systems and designs are maintenance free, here you
explain how to keep the system running.Advanced Issues(your index root)!advanced topicsYou can get most things up and running in a quick and
dirty fashion, useful for testing and getting used to how things
work. For more serious use you would need to be a little more
advanced. This is the place to explain it all, if applicable.Further Information(your index root)!information resourcesA HOWTO cannot describe everything, some times the user
has to venture out on th enet to get more information or just
updates. Here is the place to tell where and how. Again examples
from the Multi Disk HOWTO, replace as needed. There is wealth
of information one should go through when setting up a major system,
for instance for a news or general Internet service provider. The
FAQs in the following groups are useful:
News groupsdisk!information resources!news groupsSome of the most interesting news groups are:
Storage.
PC storage.
AFS.
SCSI.
Linux setup.
Most newsgroups have their own FAQ that are designed to answer most
of your questions, as the name Frequently Asked Questions indicate.
Fresh versions should be posted regularly to the relevant newsgroups.
If you cannot find it in your news spool you could go directly to the
FAQ main archive FTP site.
The WWW versions can be browsed at the
FAQ
main archive WWW site.
Some FAQs have their own home site, of particular interest:
SCSI FAQ
and
comp.arch.storage FAQ.
Mailing Listsdisk!information resources!mailing lists
These are low-noise channels mainly for developers. Think twice
before asking questions there as noise delays the development.
Some relevant lists are linux-raid,
linux-scsi and linux-ext2fs. Many
of the most useful mailing lists run on the vger.rutgers.edu server but this is
notoriously overloaded, so try to find a mirror. There are some
lists mirrored at The Redhat
Home Page. Many lists are also accessible at linuxhq, and the
rest of the web site contains useful information as well.
If you want to find out more about the lists available you can send
a message with the line lists to the list server
at majordomo@vger.rutgers.edu.
If you need help on how to use the mail server just send the line
help to the same address. Due to the
popularity of this server it is likely it takes a bit to time before
you get a reply or even get messages after you send a
subscribe command.
There is also a number of other majordomo list servers that can
be of interest such as the EATA driver list
(linux-eata@mail.uni-mainz.de)
and the Intelligent IO list linux-i2o@dpt.com.
Mailing lists are in a state of flux but you can find links to a
number of interesting lists from the
Linux Documentation
Homepage.
HOWTOdisk!information resources!HOWTOs
These are intended as the primary starting points to get the
background information as well as show you how to solve a
specific problem. Some relevant HOWTOs are
Bootdisk,
Installation,
SCSI and
UMSDOS. The main site for these is the
LDP archiveat
Metalab (formerly known as Sunsite).
There is a a new HOWTO out that deals with setting up a DPT RAID
system, check out the
DPT RAID
HOWTO homepage.
Local Resourcesdisk!information resources!local
In most distributions of Linux there is a document directory
installed, have a look in the /usr/doc
directory. where most packages store their main documentation and
README files etc. Also you will here find the HOWTO archive
(/usr/doc/HOWTO) of ready formatted HOWTOs
and also the mini-HOWTO archive
(/usr/doc/HOWTO/mini) of plain text
documents.
Many of the configuration files mentioned earlier can be found in
the /etc directory. In particular you will
want to work with the /etc/fstab file that
sets up the mounting of partitions and possibly also
/etc/raidtab file that is used for the
md system to set up RAID.
The kernel source in /usr/src/linux is, of
course, the ultimate documentation. In other words, use
the source, Luke. It should also be pointed out that the
kernel comes not only with source code which is even commented
(well, partially at least) but also an informative
/usr/src/linux/Documentation. If you are
about to ask any questions about the kernel you should read this
first, it will save you and many others a lot of time and
possibly embarrassment.
Also have a look in your system log file
(/var/log/messages) to see what is going on
and in particular how the booting went if too much scrolled off
your screen. Using tail -f /var/log/messages
in a separate window or screen will give you a continuous update
of what is going on in your system.
You can also take advantage of the /proc
file system that is a window into the inner workings of your
system. Use cat rather than
more to view the files as they are reported as
being zero length. Reports are that less works
well here.
Web Sitesdisk!information resources!WWWdisk!information resources!web pages
There are a huge number of informative web sites available. By
their very nature they change quickly so do not be surprised
if these links become quickly outdated.
A good starting point is of course the
Linux Documentation
Project home page, an information central for
documentation, project pages and much more.
Please let me know if you have any other leads that can be
of interest.
Getting Help(your index root)!assistance, obtaining
In the end you might find yourself unable to solve your problems
and need help from someone else. The most efficient way is either
to ask someone local or in your nearest Linux user group, search
the web for the nearest one.
Another possibility is to ask on Usenet News in one of the many,
many newsgroups available. The problem is that these have such a
high volume and noise (called low signal-to-noise ratio) that your
question can easily fall through unanswered.
No matter where you ask it is important to ask well or you will
not be taken seriously. Saying just my disk
does not work is not going to help you and instead the
noise level is increased even further and if you are lucky someone
will ask you to clarify.
Instead describe your problems in some detail that will enable
people to help you. The problem could lie somewhere you did not
expect. Therefore you are advised to list the following information
about your system:
HardwareProcessorDMAIRQChip set (LX, BX etc)Bus (ISA, VESA, PCI etc)
Expansion cards used (Disk controllers, video, IO
etc.)
SoftwareBIOS (On motherboard and possibly SCSI host adapters)LILO, if used
Linux kernel version as well as possible modifications
and patches
Kernel parameters, if any
Software that shows the error (with version number
or date)
Peripherals
Type of disk drives with manufacturer name, version and type
Other relevant peripherals
Remember that booting text is logged to
/var/log/messages which can answer most of
the questions above. Obviously if the drives fail you might not be
able to get the log saved to disk but you can at least scroll
back up the screen using the SHIFT and
PAGE UP keys. It may also be useful to include
part of this in your request for help but do not go overboard,
keep it brief as a complete log file dumped
to Usenet News is more than a little annoying.
Concluding Remarks(your index root)!conclusionJust summing up... Also a place for general
recommendations.Questions and Answers(your index root)!FAQ(your index root)!frequently asked questionsCheck the newsgroups and try to determine some frequent
problems and cover them here. Again an example from the Multi Disk
HOWTO.
This is just a collection of what I believe are the most common
questions people might have. Give me more feedback and I will turn
this section into a proper FAQ.
Q:How many physical disk drives (spindles) does a Linux system need?
A: Linux can run just fine on one drive (spindle). Having
enough RAM (around 32 MB, and up to 64 MB) to support swapping
is a better price/performance choice than getting a second
disk. (E)IDE disk is usually cheaper (but a little slower) than
SCSI.
Q: Are there any disadvantages in this scheme?
A: There is only a minor snag: if even a single partition
overflows the system might stop working properly. The severity
depends of course on what partition is affected. Still this is
not hard to monitor, the command df gives
you a good overview of the situation. Also check the swap
partition(s) using free to make sure you are
not about to run out of virtual memory.
Q: OK, so should I split the system into as many partitions as
possible for a single drive?
A: No, there are several disadvantages to that. First of all
maintenance becomes needlessly complex and you gain very little
in this. In fact if your partitions are too big you will seek
across larger areas than needed. This is a balance and
dependent on the number of physical drives you have.
Greg Leblanc: Depending on how big this FAQ gets, perhaps it
would be worthwhile to have, say, the 5 most FAQ, and put the
rest into an external FAQ. Dunno. Comments?
(rest deleted.)Bits and Pieces disk!miscellaneous
This is basically a section where I stuff all the bits I have not
yet decided where should go, yet that I feel is worth knowing
about. It is a kind of transient area.
Examples(your index root)!examplesExample designs and sample configuration files and other
relevant details is always handy
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