Jeff Atwood recently suffered a catastrophic loss of data of his long-running blog Coding Horror. The site was running on a virtual machine, and apparently VM backups at the hosting provider had been routinely failing for years without anybody noticing. Jeff maintained his own backups... within the VM itself, which were lost when the VM was lost. Jeff's story has a happy ending as one of his readers, Carmine Paolino, had a complete archive.
Obviously the happenstance of somebody on the Internet having a complete copy of data important to us does not constitute a practical backup strategy, but it got me to thinking about the idea of crowdsourcing backups. Everybody should have offsite backups, but practically nobody does it. Could a system be designed where each participant wanting to back up their most important data would in return offer a chunk of local disk space to use for storing data for other people?
With terabyte drives becoming common, it seems like many systems have an abundance of disk space which could be better taken advantage of. Perhaps the data you want to be backed up can be broken into chunks and stored in the free space of a number of other backup users, while your drive simultaneously stores their data.
- Your data would have to be encrypted, as it will be stored on media controlled by random and potentially untrustworthy people.
- A large amount of redundancy would have to be baked in, as people could drop out of the system at any time and take a chunk of stored information away. Many copies of each chunk would be stored in multiple places.
- Forward Error Correction would also be good, to further improve survivability in the face of missing data. Recovering most of the chunks would be sufficient to reconstruct the rest.
The practicality of the details aside, with Amazon, RackSpace and others offering cloud storage options, would it even be worthwhile to construct such a crowdsourced system? In 2010, I'm not sure that it is. I suspect this is an idea whose time has come... and gone.
Do you have tips for keeping code maintainable across multiple generations of products? This site uses 
In 1st grade I could not see how a dime could possibly be worth more than a nickel. The nickel was bigger, after all; it should obviously be worth more.
I once worked on a system where one module was developed outside using Linux/x86 systems, brought in-house, and compiled for Linux/PowerPC. We thought we had been careful in the specifications: avoid endianness assumptions, limit memory footprint, and assume a hefty derating for the slower PowerPC used in the real system. Things looked good in initial testing, but when we started internal dogfooding the PowerPC performance dropped off the proverbial cliff. An operation that took 100 msec on the x86 development system and 300 msec during initial PowerPC testing regressed to an astonishing 45 seconds in the dogfood deployment.
Amazon's 
(*) Amazon Associates link
foursquare
An interesting aspect of foursquare is the gaming angle. Badges are awarded for a huge range of activities, for example four checkins in one day earns the "crunked" badge. It looks like a drunk happy face, though in my case no alcohol was involved: 
The best experience using the service is with a GPS-enabled smartphone. There are free apps available for 
Why would investors agree to sell the company for $50 million? Presumably, they're just accepting reality. Software support businesses rarely attract venture capital, but Linux was a major buzzword for investors earlier in the decade. The trouble with support as a business model is that expenses grow linearly with revenue: as you add customers, you have to grow headcount to handle them. Expenses for a product company grow at a far slower rate, one can increase sales by 2x while increasing expenses by less than 2x.
A modern switch fabric chip is designed for both L2 ethernet switching and L3 IP routing. The additional logic for IP routing adds relatively little area in modern silicon technologies, while not having a routing capability would put them at a competitive disadvantage. Essentially all ethernet fabric chips, even those inside relatively cheap L2 switches, have the design features to route IPv4 traffic to at least a basic degree.
The fabric chip they use wasn't specifically designed for such low cost switches, there is not enough profit to justify the effort. In addition to simple L2 switches those chips can be used to build NAT appliances, as the ethernet fan-out for small wireless access points, in DSL and cable routers, for low end WAN routers, etc. When only basic L2 switching is desired these fabrics can function completely standalone without a management CPU, reducing BOM cost to the bare minimum. Addition of a CPU allows the basic L3 functions to be used in the more featureful (but still low end) products.
So, Apple is preparing to do to video distribution what it did in music, providing a complete solution including content, delivery, and customer device, right? Apple already provides selected video content on iTunes, and can expand from there.
We at Tweetravenous Solutions have another solution to offer, which allows our customers to handle a full day's work, a full day of social media, and still get a full night's sleep! We call it the Social Media Patch. Our patented algorithms will monitor your social media feeds, collating and condensing updates from those you follow and encoding them in a complex matrix of proteins, amino acids, and caffeine. Its all infused into an easy-to-apply skin patch which can be worn inconspicuously beneath clothing. Even better, its in Real Time! 
PCIe has a very high link bandwidth, making it easy to forget that its position in the system imposes several levels of bridging with correspondingly long latency to get to memory. The PCIe transaction first traverses the Northbridge and any internal switching or bus bridging it contains, on its way to the processor interconnect. The interconnect is HyperTransport for AMD CPUs, and QuickPath for Intel. Depending on the platform, the transaction might have to travel through multiple CPUs before it reaches its destination memory controller, where it can finally access its data. A PCIe Read transaction must then wend its way back through the same path to return the requested data.
For at least 15 years that I know of, chip designs have improved their yield using redundancy. The earliest such efforts were done in on-chip memory: if your chip is supposed to include N banks of SRAM, put N+1 banks on the die connected with wires in the top most layer which can be cut using a laser. The SRAM occupies a large percentage of the total chip area, statistically it is likely that defects will be within the SRAM. You can then cut out the defective bank, and turn a defective chip into one that can be used. More recent silicon processes use fuses blown by the test fixture instead of lasers.
