On 4/7/14 6:48 PM, "Ellis H. Wilson III" <[email protected]> wrote:
>On 04/07/2014 09:34 PM, Prentice Bisbal wrote: >>> Was it wear out, or some other failure mode? >>> >>> And if wear out, was it because consumer SSDs have lame leveling or >>> something like that? >>> >> Here's how I remember it. You took the capacity of the disk, figured out >> how much data would have to be written to it wear it out, and then >> divided that by the bandwidth of the drive to figure out how long it >> would take to write that much data to the disk if data was constantly >> being written to it. I think the answer was on the order of 5-10 years, >> which is a bit more than the expected lifespan of a cluster, making it a >> non-issue. > >This would be the ideal case, but requires perfect wear-leveling and >write amplification factor of 1. Unfortunately, those properties rarely >hold. > >However, again, in the case of using it as a Hadoop intermediate disk, >write amp would be a non-issue because you'd be blowing away data after >runs (make sure to use a scripted trim or something, unless the FS >auto-trims, which you may not want), and wear-leveling would be less >important because the data written/read would be large highly >sequential. Wear-leveling would be trivial under those conditions. > Wear leveling would be trivial, if one were designing the wear leveling algorithms. I could easily see a consumer device having a different algorithm from an enterprise device, either because they just spend more time and money getting a good algorithm, or because of different underlying assumptions about write/read patterns. Even in an enterprise environment, there's some very different write patterns possible. A "scratch" device might get written randomly, while a "logging" device will tend to be written sequentially. Consider something like a credit card processing system. This is going to have a lot of "add at the end" transaction data. As opposed to, say, a library catalog where books are checked out essentially at random, and you update the "check out/check in" status, and writes are sprinkled randomly through out the data. Sadly, much of this will not be particularly well documented, if at all. > _______________________________________________ Beowulf mailing list, [email protected] sponsored by Penguin Computing To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
