October 07, 2016 at 01:52AM

Today I Learned: 1) SSD drives (and presumably flash drives, too) have an interesting problem in that they read and write in entire blocks of .5-1 megabytes. When a write happens, the entire block is actually read, modified, and written back in. That's particularly annoying since flash memory wears out with use, and too many read/write cycles to a single memory location will break it. Accordingly, SSD manufacturers have a lot of tricks for reducing write requirements. Also, SSDs come with a bit of extra memory onboard. When blocks break, they can detect the fault, permanently lock out that block, and allocate to one of the reserve blocks instead. 2) So, how long do SSDs last? This (http://ift.tt/2cWbdkE) delightful experiment from last year pushed six commercial SSDs to their deaths. According to the authors, SSD manufacturers guarantee their drives to about 20 TB of read/writes, or 20 GB/day for three years. In fact, they perform well for much, much longer -- of the six drives tested, none hit a single error until around the 100th terabyte. *That* drive continued to funciton, albeit with increasingly smaller storage capacity, until between 800 and 900 total writes. Other drives performed better, logging hundreds of terabytes before their first failure and the best writing over a petabyte before finally crashing for good. Not bad. Thanks to Chris Lennox for finding this! *Just a warning, when I left a tab with this article open for a while, it started sucking up memory and processing time. By the time I killed it it was using several gigabytes of RAM. Not sure if that was a bug or some kind of background process, but I thought you should be aware. Can anyone replicate? 3) There is a species of parasitic wasp that lays its eggs in caterpillars... you know, there are a lot of great evolutionary stories that start that way, or at least very similarly. Anyway. This *particular* species has a weird quirk that their young hatch together as a brood and then immediately mate with any wasp around, which is usually siblings. Yes, it's odd that they're so inbred, but there you have it. This mating system has an interesting consequence for optimal sex ratio choice. If all of your children are mating with your own children, then it turns out the best sex ratio strategy is to have almost entirely female children, and just a couple of males that can fertilize them all. That way, you have the most possible opportunities for grandchildren. This is, in fact, what this wasp does -- it can control the male-to-female ratio of its broods, and it prefers to lay broods with lots and lots of females. That changes if the wasp lays a brood in a caterpillar that already has another set of eggs in it. In this case, the wasp's male children have to compete with the first mother's (few) male children. The payoff for having males is suddenly higher, because it increases the chances of fertilizing all the copious numbers of females that will be around, which is really efficient. The second wasp will lay a brood with a higher ratio of males to females. As more and more wasps lay their eggs in the same food source, the ratio of males increases, eventually approaching 50%. Amazingly (or, perhaps, quite expectedly), you can calculate the game-theoretic optimal ratio of males in a brood for any number of previous broods layed in the same caterpillar, and the behavior of this wasp matches the theoretical results quite well.