ugh, hit the wrong key and sent unfinished mail. holding a baby. --Z
On Wed, Dec 9, 2009 at 8:46 AM, Zooko O'Whielacronx <[email protected]> wrote: > Oh by the way there is another cool thing you can do if you do have > "proximity awareness": save the bandwidth costs of repair. Suppose > you have a petabyte worth of hard drives -- e.g. 500 hard drive each > of 2 TB. Hard drives fail at a rate of around 6% per year [1], so you > would expect about 30 of them to fail per year, which is about one > every two weeks. > > > Suppose you have three locations which have very fast and cheap > bandwidth within the location, e.g. the LAN connecting different > servers in the same rack, but slower and more expensive bandwidth > between locations, e.g. if you have to pay a per-bandwidth fee to > transmit between co-lo's. Then let's call "Q" the number of > locations, and you should set your N value to be (K+1) * Q. For > example, if K is 3 (three shares needed to reconstruct a file), and Q > is 3 (three locations), then set your N equal to 12 and (once we > implement "proximity awareness"), make sure that there are four shares > in each location. > > The advantage of this is that it makes repair cheap. Suppose you have a > > [1] Eduardo Pinheiro, ~Wolf-Dietrich Weber, and Luiz André Barroso > (all of Google Inc.): Failure Trends in a Large Disk Drive Population > http://labs.google.com/papers/disk_failures.pdf > _______________________________________________ tahoe-dev mailing list [email protected] http://allmydata.org/cgi-bin/mailman/listinfo/tahoe-dev
