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4. Set up, configuration, and maintenance

4.1 Disk configuration

This section describes disk partitioning strategies. Our goal is to keep the virtual structures of the machines organised such that they are all logical. We're finding that the physical mappings to the logical structures are not sustainable as hardware and software (operating system) change. Currently, our strategy is as follows:

farm/cluster machines:

partition 1 on system disk     - swap  (2 * RAM)
partition 2 on system disk     - /     (remaining disk space)
partition 1 on additional disk - /maxa (total disk)

servers:

partition 1 on system disk        - swap  (2 * RAM)
partition 2 on system disk        - /     (4-8 GB)
partition 3 on system disk        - /home (remaining disk space)
partition 1 on additional disk 1  - /maxa (total disk)
partition 1 on additional disk 2  - /maxb (total disk)
partition 1 on additional disk 3  - /maxc (total disk)
partition 1 on additional disk 4  - /maxd (total disk)
partition 1 on additional disk 5  - /maxe (total disk)
partition 1 on additional disk 6  - /maxf (total disk)
partition 1 on additional disk(s) - /maxg (total disk space)

desktops:

partition 1 on system disk        - swap   (2 * RAM)
partition 2 on system disk        - /      (4-8 GB)
partition 3 on system disk        - /spare (remaining disk space)
partition 1 on additional disk 1  - /maxa  (total disk)
partition 1 on additional disk(s) - /maxb  (total disk space)

Note that in the case of servers and desktops, maxg and maxb can be a single disk or a conglomeration of disks.

4.2 Package configuration

Install a minimal set of packages for the farm. Users are allowed to configure desktops as they wish, provided the virtual structure is kept the same described above is kept the same.

4.3 Operating system installation and maintenance

Personal cloning strategy

I believe in having a completely distributed system. This means each machine contains a copy of the operating system. Installing the OS on each machine manually is cumbersome. To optimise this process, what I do is first set up and install one machine exactly the way I want to. I then create a tar and gzipped file of the entire system and place it on a bootable CD-ROM which I then clone on each machine in my cluster.

The commands I use to create the tar file are as follows:

tar -czvlps --same-owner --atime-preserve -f /maxa/slash.tgz /

I use a script called go that takes a machine number as its argument and untars the slash.tgz file on the CD-ROM and replaces the hostname and IP address in the appropriate locations. A version of the go script and the input files for it can be accessed at: http://www.ram.org/computing/linux/linux/cluster/. This script will have to be edited based on your cluster design.

To make this work, I use Martin Purschke's Custom Rescue Disk ( http://www.phenix.bnl.gov/~purschke/RescueCD/) to create a bootable CD image containing the .tgz file representing the cloned system, as well as the go script and other associated files. This is burned onto a CD-ROM.

There are several documents that describe how to create your own custom bootable CD, including the Linux Bootdisk HOWTO ( http://www.linuxdoc.org/HOWTO/Bootdisk-HOWTO/), which also contains links to other pre-made boot/root disks.

Thus you have a system where all you have to do is insert a CDROM, turn on the machine, have a cup of coffee (or a can of coke) and come back to see a full clone. You then repeat this process for as many machines as you have. This procedure has worked extremely well for me and if you have someone else actually doing the work (of inserting and removing CD-ROMs) then it's ideal. In my system, I specify the IP address by specifying the number of the machine, but this could be completely automated through the use of DHCP.

Rob Fantini ( rob@fantinibakery.com) has contributed modifications of the scripts above that he used for cloning a Mandrake 8.2 system accessible at http://www.ram.org/computing/linux/cluster/fantini_contribution.tgz.

Cloning and maintenance packages

FAI

FAI ( http://www.informatik.uni-koeln.de/fai/) is an automated system to install a Debian GNU/Linux operating system on a PC cluster. You can take one or more virgin PCs, turn on the power and after a few minutes Linux is installed, configured and running on the whole cluster, without any interaction necessary.

SystemImager

SystemImager ( http://systemimager.org) is software that automates Linux installs, software distribution, and production deployment.

DHCP vs. hard-coded IP addresses

If you have DHCP set up, then you don't need to reset the IP address and that part of it can be removed from the go script.

DHCP has the advantage that you don't muck around with IP addresses at all provided the DHCP server is configured appropriately. It has the disadvantage that it relies on a centralised server (and like I said, I tend to distribute things as much as possible). Also, linking hardware ethernet addresses to IP addresses can make it inconvenient if you wish to replace machines or change hostnames routinely.

4.4 Known hardware issues

The hardware in general has worked really well for us. Specific issues are listed below:

The AMD dual 1.2 GHz machines run really hot. Two of them in a room increase the temperature significantly. Thus while they might be okay as desktops, the cooling and power consumption when using them as part of a large cluster is a consideration. The AMD Palmino configuration described previously seems to work really well, but I definitely recommend getting two fans in the case--this solved all our instability problems.

4.5 Known software issues

Some tar executables apparently don't create a tar file the nice way they're supposed to (especially in terms of referencing and de-referencing symbolic links). The solution to this I've found is to use a tar executable that does, like the one from RedHat 7.0.


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