Thin Clients Booting over a Wireless Bridge
The boot process of a thin client is network-intensive, but once the operating system has been transferred, there is little traffic between the client and the server. As the time required to boot a thin client is a good indicator of the overall usability of the network, this is the metric we used in all our tests.
Our testbed consisted of a 3GHz Pentium 4 with 1GB of RAM as the PXE server. We chose Edubuntu 5.10 for our server, as this (and all newer versions of Edubuntu) come with LTSP included. We used six identical thin clients: 500MHz Pentium III machines with 512MB of RAM—plenty of processing power for our purposes.
When performing our tests, it was important that the results obtained were free from any external influence. A large part of this was making sure that the wireless bridge was not affected by any other wireless networks, cordless phones operating at 2.4GHz, microwaves or any other sources of Radio Frequency (RF) interference. To this end, we used the Azimuth 301w Test Chamber to house the wireless devices (see Resources). This ensures that any variations in boot times are caused by random variables within the system itself.
The Azimuth is a test platform for system-level testing of 802.11 wireless networks. It holds two wireless devices (in our case, the devices making up our bridge) in separate chambers and provides an artificial medium between them, creating complete isolation from the external RF environment. The Azimuth can attenuate the medium between the wireless devices and can convert the attenuation in decibels to an approximate distance between them. This gives us the repeatability, which is a rare thing in wireless LAN evaluation. A graphic representation of our testbed is shown in Figure 2.
We tested the thin-client network extensively in three different scenarios: first, when multiple clients are booting simultaneously over the network; second, booting a single thin client over the network at varying distances, which are simulated by altering the attenuation introduced by the chamber; and third, booting a single client when there is heavy background network traffic between the server and the other clients on the network.
As shown in Figure 3, a wired network is much more suitable for a thin-client network. The main limiting factor in using an 802.11g network is its lack of available bandwidth. Offering a maximum data rate of 54Mbps (and actual transfer speeds at less than half that), even an aging 100Mbps Ethernet easily outstrips 802.11g. When using an 802.11g bridge in a network such as this one, it is best to bear in mind its limitations. If your network contains multiple clients, try to stagger their boot procedures if possible.
Second, as shown in Figure 4, keep the bridge length to a minimum. With 802.11g technology, after a length of 25 meters, the boot time for a single client increases sharply, soon hitting the three-minute mark. Finally, our test shows, as illustrated in Figure 5, heavy background traffic (generated either by other clients booting or by external sources) also has a major influence on the clients' boot processes in a wireless environment. As the background traffic reaches 25% of our maximum throughput, the boot times begin to soar. Having pointed out the limitations with 802.11g, 802.11n is on the horizon, and it can offer data rates of 540Mbps, which means these limitations could soon cease to be an issue.
In the meantime, we can recommend a couple ways to speed up the boot process. First, strip out the unneeded services from the thin clients. Second, fix the delay of NFS mounting in klibc, and also try to start LDM as early as possible in the boot process, which means running it as the first service in rc2.d. If you do not need system logs, you can remove syslogd completely from the thin-client startup. Finally, it's worth remembering that after a client has fully booted, it requires very little bandwidth, and current wireless technology is more than capable of supporting a network of thin clients.
Practical Task Scheduling Deployment
July 20, 2016 12:00 pm CDT
One of the best things about the UNIX environment (aside from being stable and efficient) is the vast array of software tools available to help you do your job. Traditionally, a UNIX tool does only one thing, but does that one thing very well. For example, grep is very easy to use and can search vast amounts of data quickly. The find tool can find a particular file or files based on all kinds of criteria. It's pretty easy to string these tools together to build even more powerful tools, such as a tool that finds all of the .log files in the /home directory and searches each one for a particular entry. This erector-set mentality allows UNIX system administrators to seem to always have the right tool for the job.
Cron traditionally has been considered another such a tool for job scheduling, but is it enough? This webinar considers that very question. The first part builds on a previous Geek Guide, Beyond Cron, and briefly describes how to know when it might be time to consider upgrading your job scheduling infrastructure. The second part presents an actual planning and implementation framework.
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With all the industry talk about the benefits of Linux on Power and all the performance advantages offered by its open architecture, you may be considering a move in that direction. If you are thinking about analytics, big data and cloud computing, you would be right to evaluate Power. The idea of using commodity x86 hardware and replacing it every three years is an outdated cost model. It doesn’t consider the total cost of ownership, and it doesn’t consider the advantage of real processing power, high-availability and multithreading like a demon.
This ebook takes a look at some of the practical applications of the Linux on Power platform and ways you might bring all the performance power of this open architecture to bear for your organization. There are no smoke and mirrors here—just hard, cold, empirical evidence provided by independent sources. I also consider some innovative ways Linux on Power will be used in the future.Get the Guide