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This isn't 'How to Think Like A Computer Scientist', but rather 'Introducing Programming with Python'.

It's a good introductory text for learning Python. However programming is a very small part of Computer Science.

http://abstrusegoose.com/strips/computer_science_major.PNG



Doesn't seem like diatomaceous earth would help much with bedbugs.

DDT actually wasn't all that bad. The problem was that it was way way way overused (back in the fifties they were literally pouring thousands of gallons into lakes and rivers because they thought it would be a good idea to get rid of the mosquitos).


Yeah, a closed source application installed as root, with the express purpose of accessing your webcam and microphone. What could go wrong?


Here's the header of the /etc/crontab.daily/google-talkplugin file. I'm not that ninja with my cron-tabbing, but doesn't this do exactly what it says?

http://pastebin.com/4etPxNWC


Yes, and it's pretty much harmless in itself, but since when does installing one package (esp. from a third party with no verification beforehand) install a new apt key into your keyring (thus allowing all packages signed by that key, no matter what they are) and reconfigure the package manager itself? It's ludicrous.


It's probably a mistake, and they'll put some prompts and options in once they realize Linux users don't like giving root so freely.

They're probably accustomed to trusting their own software with root, so didn't even think about it.


It's not a mistake: the development deb for Chrome did exactly this - installed the repository key and a cron job to "protect" the apt-sources entry. Of course it's not really doing this secretly, in that you can read about it in the post-install script before you run dpkg, but I agree it doesn't feel right.

Also, can't this be said of any package you install through the package manager? If you install it as root, then in principle you're giving root access to whatever is in the package. If you don't like it, there's always a way to run it with ordinary permissions (but the extra fiddling to get that working may be hairy) or under mandatory access control (definitely hairy).


It's probably a mistake

Nah, it was probably just developed for internal Google consumption.


It really depends on the platform and requirements.

On a desktop, a three-drive RAID0 provides about the same performance, and gives you nearly 40x the storage for a given price-point.

On a mobile platform the physical space, vibration/motion, and power constraints coupled with the increased performance may make SSDs worthwhile.


On a desktop, a three-drive RAID0 provides about the same performance, and gives you nearly 40x the storage for a given price-point.

Quite a terrible idea unless you enjoy backup recovery sessions.

If the noise of 3 drives doesn't bother you then you can just as well get 4 and setup a RAID10, which is nearly as fast but much less likely to fail.


I back up several times a day, automatically. I've run RAID arrays for years with no problems, but all drives eventually fail. An SSD is internally a RAID0 that can be up to 16 wide (that's how they get their performance). Used and managed properly (including proper backup and recovery), RAID0 works very well with good quality drives. If you have noise problems, then you likely have vibration issues that will shorten the life of your drives. I use anti-vibration mounts for all hard drives, and I hear my (quiet, anti-vibration mounted) fans more than I hear my drives. I also spin down the backup drives when they are not in use, so they add no additional noise.


An SSD is internally a RAID0 that can be up to 16 wide (that's how they get their performance).

Erm. Actually they get their performance because they write to NAND instead of spinning platters. SSD controllers are also quite a bit smarter than plain RAID0.

RAID0 works very well with good quality drives.

A RAID0 over three disks has about 1/3 the MTBF of a single disk.

That can still be a worthwhile trade-off if you need the extra capacity, but if you're mostly after performance and reliability then a pair of SSDs, or even a single SSD, is the better choice.


You'll probably find this interesting reading on the internal architecture of SSDs:

     http://www.denali.com/wordpress/index.php/dmr/2010/02/02/ssd-interfaces-and-performance-effects
Also, while RAID0 reduces the MTBF, it's not linear. Drive life is not magically shortened as a result of the drive being in a RAID array (if you take care to isolate synchronous vibration). The life of the array is equal to the shortest drive life. In other words, if a drive would have failed after 25,000 hours in standalone operation, it will still fail in 25,000 hours in an array. The other drives may run to 100,000 hours, but it's a "weakest link" failure mode.


Also, while RAID0 reduces the MTBF, it's not linear.

Well, it is inverse proportional.

The life of the array is equal to the shortest drive life.

Erm. To be clear: Your risk of having a RAID0-set (over 3 disks) fail during a given timespan is 3 times higher than having a single-disk-"set" fail in the same timespan.

In other words, if a drive would have failed after 25,000 hours in standalone operation, it will still fail in 25,000 hours in an array.

That calculation makes no sense. If you have a single drive then that will fail, on average, after 25k hours. If you stripe over three of these drives then your array will, on average, fail after 8333 hours.


While the probability of failure is nearly a function of the number of drives, the MTBF/MTTF calculations do not work that way.

For example, if there were a probability of 5% that the disk would fail within three years, in a three disk RAID0 array, that probability of failure would be:

P=(1-(1-.05)^3)=.14263

In other words, 14.3% probability of failure within three years. That doesn't mean it will fail in that time frame. It means if you have a large population of that configuration, that is the rate you would be dealing with for drive replacement planning.

The MTBF and MTTF calculations apply to populations of drives (e.g. a given model) not to a given drive. The values provide no predictability for the failure of any specific drive. Using the values for that purpose is a common misapplication. A drive with a MTTF of 1,000,000 power-on hours can fail in 15 minutes or never during its useful life.

As a result, a three drive array will have a higher probability of failure over a given interval, but the MTTF/MTBF of the drives is essentially unchanged.

Think of it this way... The probability of winning the lottery is one in 20,000,000. The probability that someone (anyone) will win the lottery in a given week may be one out of ten - 10%. In other words, some person wins the lottery, on average, one time in ten weeks. That doesn't mean that your probability of winning the lottery is 10%. It also doesn't mean that the average probability of winning the lottery is 10%. It also doesn't change the probability of winning the lottery; it's still one in 20,000,000, even if three people win in a 10 week interval.


Hm. Thanks for repeating what I just said, I guess. But what was your point again?


tl;dr: For RAID0 arrays there is a non-linear increase in the probability of failure, but the MTTF/MTBF doesn't change much.


Could it be you're just arguing for arguments sake?

My original point was: A RAID0 over 3 disks is about 3 times more likely to fail than a single disk running standalone. Fail means "total data loss". You confirm that point with your own math, yet still seem to be trying to argue that there was no difference. Sorry, that makes no sense to me.


Your statement was:

"A RAID0 over three disks has about 1/3 the MTBF of a single disk."

This is incorrect, the MTTF and MTBF are not significantly changed. Assuming you meant failure probability, my issue with the probability variance is the linear relationship you imply.

If the variation were linear, a RAID array composed of drives with a 5% failure probability would reach certainty of failure (1.00 probability) within the interval at 20 drives. In actuality, it takes 225 drives to reach that probability.

The difference is a real world consideration for capacity management. What it means is that RAID0 arrays are not as failure prone as people think they are.


> "A RAID0 over three disks has about 1/3 the MTBF of a single disk." This is incorrect, the MTTF and MTBF are not significantly changed.

Wikipedia disagrees; http://en.wikipedia.org/wiki/Standard_RAID_levels#RAID_0_fai...

array_MTTF = avg(drive_MTTF) / number_of_drives


Which is at odds with the (correct) definition of MTTF as a rate-based calculation:

http://en.wikipedia.org/wiki/Failure_rate

The person that wrote the Wikipedia article you referenced read the same mythology you did; repeating it doesn't make it true. The plural of anecdote is not fact.

Think about it yourself for a moment. If two cars are traveling 50mph, does that make their average speed 25mph (50/2)? Applying a divisor to a failure rate based on the number of devices is nonsensical.


If you are so convinced then why don't you correct the wikipedia article?

Perhaps also call up LSI and Adaptec, who use the same formula in their documentation.

http://storageadvisors.adaptec.com/2005/11/01/raid-reliabili...

But what do they know, they only build raid controllers...


You're right, there's no reason to try to correct the 20% of the population that believes the Sun revolves around the Earth. It's a lost cause; you win.


You're right, there's no reason to try to correct the 20% of the population

Erm wait, didn't I just suggest the exact opposite?

If you really think everyone has been wrong about this all the time then please, by all means, correct wikipedia or write a blog post about the matter.

This "false" formula has been out there for quite some time and you find it in pretty much every write-up on the topic, including those from RAID-vendors who (I'd hope) have spent some thought on these things.

On the flip-side I haven't found a single source to support your thesis. Thus I'd say the burden of proof is on you.


Make friends with spiders and house centipedes. They are the natural enemies of most every house pest, including bedbugs, and mostly harmless to people. The enemy of my enemy is my friend.


Model numbers? Isn't that why UUIDs were created? Unique identifier, and anonymous:

https://secure.wikimedia.org/wikipedia/en/wiki/UUID


"The customer didn't really want to use a unique identifier though, because though it was anonymous, the customer wanted to count computers, but unique identifiers are for tracking (following a user over time)."


That seems to be a misunderstanding of the nature of a UUID. Simply replacing the model with the UUID provides no tracking in this use case, as it's a single purpose reference.


I can't figure out what exactly you are proposing here..

If you propose that they generate a new UUID on every ping the OS makes, then you'd be able to tell how many unique installations are active on any given day, but you wouldn't know how long they had been active, nor would you know what model of computer they were, nor would you be able to know how many were active for a longer time range such as a week or a month.


Fedora, for example, already does this with UUIDs and the smolt project. A UUID is generated on installation and used for the 'ping'. The user opts-in at first boot, and the software runs periodically:

http://en.wikipedia.org/wiki/Smolt_(Linux)

The data is aggregated for reporting:

http://www.smolts.org/


So women are only permitted to search for men? No lesbians allowed? After the eHarmony lawsuit and $500,000 payout, you'd think dating sites wouldn't want to repeat that disaster.


Lawsuits like that are stupid as I'm sure if you were straight you couldn't sue a homosexual dating site!


too right! lawsuit in the making!


As background, from WikiPedia:

"On November 13, 2006, Sun released much of Java as open source software under the terms of the GNU General Public License (GPL). On May 8, 2007, Sun finished the process, making all of Java's core code available under free software/open-source distribution terms, aside from a small portion of code to which Sun did not hold the copyright."

If Sun willingly made the code GPL licensed, and Google isn't using anything outside the GPL code, even if some of the technologies were covered by patents I don't see Oracle having a case. Right now, this sounds very much like the SCO - Linux suit that dragged on forever and went nowhere.


Google is using NONE of the Sun code. They use their own VM, and use the Apache Harmony class libraries. That's why it isn't called "Java"

The Sun release has some weird field-of-use restrictions associated with it.


Giving out software under the GPL v2 does not mean that you grant others a patent license, that isn't within the scope of the GPL v2.


That's not true. See section 7 of the GPL. In part:

For example, if a patent license would not permit royalty-free redistribution of the Program by all those who receive copies directly or indirectly through you, then the only way you could satisfy both it and this License would be to refrain entirely from distribution of the Program.

However, it seems Sun can relicence the software under whatever they want, and the current versions of it wouldn't be under GPL anymore. I am not a lawyer, so I don't know exactly what this implies.


So you're saying that it grants users of the GPL code an exception from the patent owned by the original developers?

In that case, wouldn't the exception only be extended to Google if their implementation of Java was not independent from Sun's implementation? Because Devrak was derived from Apache Harmony, it might not share any code with Oracle Java.


"However, it seems Sun can relicence"

You mean Oracle, of course, and that seems to make a big difference.


Considering that Sun released Java before the GPL v3 was finished, I assume that it's under the GPL v2. v2 doesn't have the same patent guarantees that v3 does, and these guarantees were an important reason for creating v3. Specifically, the GPL v3 specifically prohibits this sort of "make it free software and then sue over the patents". The GPL FAQ claims that in some countries, releasing software under the GPL v2 constitutes a patent license, but I don't think that applies in the US.


There's no need to assume when authoritative information is but a few keystrokes away. And yes, it is under the GPL v2 + Classpath exception, except for Java ME which is under straight GPL v2.


Exactly this is the core question here.

I am really curious about how the law sees this.

And I would really wonder if they decide against Google. It looks almost like a trap of Sun/Oracle then, kind of "hey, here, use our code, it is open source now grin".

Or to put it different: Why did they use the GPL licence?


I actually have no problem with Apple's prices. People don't buy a Rolls-Royce because it's a car, they buy it because it's a Rolls-Royce. Comparing the purchase price or mpg to a Toyota Camry is missing the point.

I build my own machines, and don't buy Apple products. However, I see nothing wrong with charging what the market will bear for an upscale product.


Why does everyone forget that copyrighted content can be shared if the license allows it? Copyright does not automatically prohibit sharing.

   http://creativecommons.org/about/
   http://www.opensource.org/licenses/alphabetical
The real problem is that content creators frequently don't make finding the license easy - if they even use one.


How is that the real problem?

Who said anyone forgot? The article doesn't. It clearly says the author of the content found their work being shared without consent.

The real problem is someone is ripping off someone else's work.

Leaving aside the never ending discussion on piracy, I don't get what your point is.


My comment was in reply to the author's statement that "sharing a copyrighted design is theft". This is clearly false.


The author also complained about free designs:

"not merely because designs are being “shared” (read “pirated”), but because people are downloading free charts rather than paying for a designer’s work."

At least, that's how I read it.


Pretty sure the real problem with that theory is those aren't the licenses most people choose.

Movies, software and games that are non-distributable have significant signs or precautions in place advertising that. The only thing that doesn't is music.


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