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At least in my personal opinion, one of the strongest trends seen at the LinuxWorld expo in San Francisco over the last years has been virtualization. This year many exhibitors had taken the next step and were actually using VMware products on their exhibit computers to simulate a number of servers in a network. For instance, Hyperic demoed their systems management software with a set of virtual servers.

Whenever virtualization comes up, the idea of grid computing isn’t far away as enterprises wish to maximize server utilization by turning their data centers into grids that each deliver the ‘services’ of CPU, memory, ports and so on. But in this brave new world of virtual machines and grid processing there is an element missing. If you’re moving your computing over to a grid computing model, why is there no corresponding grid storage model?

The commercial open source startup Cleversafe has that corresponding model. By employing a mathematical algorithm known as an Information Dispersal Algorithm, found in the cryptographic field of research, Cleversafe separates data into slices that can be distributed to different servers, even across the world. But it’s much more than just slicing and dicing: the algorithm adds redundancy and security as it goes about its task. When the algorithm is done, each individual slice is useless in isolation, and yet not all slices are needed to reconstruct the original data. In other words, your data is safer both in terms of security and in terms of reliability.

Cleversafe is not the first entity to come up with such a scheme. The idea of an Information Dispersal Algorithm is known from Adi Shamir’s paper ‘How to Share a Secret’ and other publications. When we met up with Cleversafe’s Chairman and CTO Chris Gladwin at LinuxWorld, he mentioned that the Information Dispersal Algorithm had been used in many applications before – even to store launch codes for nuclear weapons securely.

The scheme is different from a simple parity scheme in that you can configure how many redundant pieces you want. With parity as found in common RAID setups, you can lose any one storage unit in the set. With an Information Dispersal Algorithm, you can make your system resistant to failure or corruption of any one, two or indeed any number of units in the set. If there’s a strike in your data center in Texas, and your German data center is on fire, your data will still be fully accessible through the remaining servers provided you began with a sufficient number of servers. And as opposed to the brute force solution of multiple mirrors of the data, the dispersal algorithm has a much smaller overhead.

Google is a well known proponent of the brute force solution: the Google File System implementation suggests that the best method to keep your data continuously available is to keep three copies of it at all times. Cleversafe is a smarter system. If you have 16 slice servers (known as pillars in Cleversafe terminology) with a redundancy of 4 slices (known as the threshold) you can lose up to four servers simultaneously and still retain your data. At the same time the total overhead in storage space is only 4/12 – 33% of the space. The advantage as compared to Google’s three copies method is clear: with three copies you only protect yourself against the failure of any two servers and yet you pay a much greater price with a total of 200% storage and bandwidth overhead. And that’s not all. While you’re storing two additional copies of your data, you have effectively tripled the risk of that data being stolen. When a careless system administrator forgets the backup tapes in his car over night and the car gets stolen, all those credit card numbers or what have you will be out in the wild, even that only one out of three locations was compromised. In our Cleversafe example, 12 separate servers would have to simultaneously be compromised – quite unlikely by comparison.

Cleversafe is not alone and there are other actors on the software market such as the PASIS system. PASIS’ home page describes functionality very similar to Cleversafe’s: “PASIS is a survivable storage system. Survivable storage systems can guarantee the confidentiality, integrity, and availability of stored data even when some storage nodes fail or are compromised by an intruder.” None the less, Cleversafe appears to be a step ahead of its competitors at this time and is poised to be the first to deliver grid storage to a wider market.

While the Cleversafe software is developed as open source through the Cleversafe Open Source Community at, there is a commercial company behind Cleversafe: Cleversafe, Inc. Cleversafe, Inc. plans to generate revenue by offering a storage grid for rent based on the Cleversafe technology. “The market for a more secure, more cost effective storage solution is enormous,” says Jon Zakin, CEO of Cleversafe in a press release issued in May.

The Cleversafe project is available as Open Source under the GPL 2.0 License. The version online is apparently an early alpha version and is not ready for production use. According to Mr. Gladwin, there will most likely be a new version within a month, and sometime in the beginning of the next year Cleversafe may be ready for production use. In the meantime, you can download the current alpha version of the software at the Cleversafe Open Source Website. You can read more about the algorithm at’s wiki, and there’s also a flash video describing the idea available.

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Introducing YippieMove '09. Easy email transfers. Now open for all destinations.

Yahoo! recently released a new Firefox extension called YSlow. This article describes how to get started and what we did at Playing With Wire to get our front page to load in almost half the time.

YSlow is a handy little tool for analyzing the performance of your websites. It will give you vital statistics and grade your site on 13 performance points with helpful hints for what you may be able to do to improve the loading speed of your pages.


YSlow is actually a plugin to a plugin in Firefox. To use it, you need Firefox and the Firebug web developer plugin. Both are easily installable using links from YSlow’s homepage however.

Once you’ve restarted Firefox with the new plugins installed, all you have to do is to activate Firebug for a particular site and you’re ready to go. Normally, this means surfing to the site and then revealing Firebug from its icon in the Firefox status bar. Just click the Firebug icon and it will reveal it’s main view. In it, it will most likely say that Firebug is disabled. Just click ‘Enable Firebug for this web site’ and you’re ready to start dissecting it’s performance with Yahoo!’s YSlow.

This is what Firebug looks like.
Firebug revealed.

Taking your site apart

Once you have Firebug enabled, switch to the ‘Performance’ tab and you’ll get a grade on your website’s loading performance. The grade breaks down into several subcomponents where each one corresponds to a point in Yahoo!’s Thirteen Simple Rules for Speeding Up Your Web site. The grading is fairly arbitrary and should be taken with a grain of salt. For example, if you have 35 downloads for your page and just four of them don’t have an Expires header, YSlow will give you a harsh F in that category.

YSlow gives Playing With Wire an F for Expires headers.
Hello, is this Google? YSlow is giving me an F in Expires headers. Could you reconfigure your ad servers for me?

None the less, the sub-points of the grade-sheet are great hints for what you can do with your site. While you’ll probably be forced to ignore the ‘grades’ if you have externally sourced ad units like we do, you can still work your way through the list and fix everything that you do have control over. This is what we did with Playing With Wire and astonishingly enough we reduced the download size to about half of what it used to be. Below are the best tricks we learnt or revisited after using YSlow.

Eliminate HTTP requests

This is a well known method that we had already worked into the design of Playing With Wire. The idea is to have as few CSS, image and Javascript files as possible. Most browsers will only download two files at a time and there’s always some overhead associated with the download of a new file. If you can combine files you reduce this overhead.

YSlow’s Components page let us know exactly what we were bringing in through links and we could eliminate an external Javascript we were no longer using.

Add Expires headers

Expires headers are important to let web browsers know that once they’ve cached an image, CSS include or Javascript file, they can keep using it for a while. Without these headers most browsers will keep downloading the same files over and over out of fear that they may change frequently. Again, YSlow’s Components tab reveals relevant information: the Expires column lets you know what Expiry date your web server is broadcasting for each downloaded file. If you notice files with a value in the Expires column, it may be time to go into your web server configuration file. In Apache, a section like this one might just do the trick:

<virtualhost ...>

<directory ...>
  ExpiresByType text/css "access plus 1 week"
  ExpiresByType text/javascript "access plus 1 week"
  ExpiresByType image/gif "access plus 1 week"
  ExpiresByType image/jpg "access plus 1 week"
  ExpiresByType image/jpeg "access plus 1 week"
  ExpiresByType image/png "access plus 1 week"

  ExpiresActive On

Enable compression

Most modern clients support streaming compression. This is a feature that lets the web server compress data before sending it to the client. This reduces the download time of the page at the expense of some CPU time on the server. While most graphics can’t be compressed much, this turns out to work out great for HTML, CSS and Javascript. All of these files can often be reduced to as little as a third of their original size. The best part is that the web server won’t try to compress the data unless it already knows the client can handle it.

How to set up compression depends on your application and web server software. If you’re using Apache, you can have the server do it for you for normal files. For dynamic content such as that generated by PHP it depends. In WordPress there’s a switch in the Options tab. If you’re using wp-cache like Playing With Wire is, it may take some more work to get things up and running, but it’s well worth the effort.


Between these tricks and a couple more, Playing With Wire came out about half as heavy for the main HTML, CSS and Javascript, and as a result felt much more responsive. All in all YSlow was a helpful utility, especially thanks to its ‘Components’ tab which made it easy to see what parts of the page were being cached and compressed properly, and which ones were not. The grading system wasn’t very helpful, not all of the grade hints were applicable, and none of the hints were unknown in the field. Still, the list of suggestions was a useful as a kind of laundry list of things to do for the site, combined with data specific to your site. At the end of the day, I’ve found a new partner for optimizing websites with Yahoo!’s YSlow.

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Introducing YippieMove '09. Easy email transfers. Now open for all destinations.

The articles here at PWW tend to be a bit more in depth than this, but I thought this might be a good tips that many would benefit from. As you’ve probably figured out by now, both Alex and I are Mac users, and just adore the design of Apple’s products. As a result of this, both Alex and I bought the Wireless Mighty Mouse to use with our laptops. A couple of days ago my Mighty Mouse stopped scrolling up. It was weird, because I could still scroll down and horizontally. Since this was very annoying, it became the first thing on my priority list to fix.

After some googlin’ and reading on a couple of Mac forums, I found the solution. Press down the ‘scroll ball’ hard. This sounds like a weird thing to do, but after checking some other sites that said the same thing, I tried it. After pressing the ‘scroll ball’ down quite hard the scroll feature started working again.

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Introducing YippieMove '09. Easy email transfers. Now open for all destinations.
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I’ve been using Windows Vista on occasion recently. When I used it for the first time, I was expecting to see the now infamous ‘Cancel or allow?’ dialog boxes popping up left and right. To my surprise there was nothing of the sort. It took me a moment and to realize that the default account that had been created for me in Vista was an ‘administrator’ account, which allows you to do anything.

I’m not really sure why this is the default account. It’s like your Linux box would log you in as root by default. But fair enough, if that’s the Vista way, that’s the Vista way. I went ahead and created a normal account for myself and logged into that account instead.

Everything was well until I restarted my Vista machine the next time. I found myself right back in the administrator account. Apparently Vista insists that Administrator is the right account to be in.

To make a long story short, it took me just about forever to figure out how to make Vista not log me in automatically this way. I’m going to post it here to help other people with the same problem.

  1. Pull up the Run… menu (Windows + R on the keyboard)
  2. Enter “netplwiz” and click “Ok”.Windows Vista Run Menu.
  3. Check the “Users must enter a user name and password to use this computer” checkbox.Advanced User controls in Windows Vista.

Hope that helps someone. It’s hard to find for sure. You can also check the box, and then click on another account name in the list, thus selecting it. Then uncheck the box again and you’ll be asked for the password for that account – now the selected account is your new default account. If you make this a non administrator account you should have increased your security a little bit during day to day computer use.

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