Changes between Version 71 and Version 72 of FAQ


Ignore:
Timestamp:
2012-04-18T21:54:14Z (10 years ago)
Author:
zooko
Comment:

link to wiki page on server selection

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  • FAQ

    v71 v72  
    7272'''[=#Q12_server_location_distribution Q12:] If I had 3 locations each with 5 storage nodes, could I configure the grid to ensure a file is written to each location so that I could handle all servers at a particular location going down?'''
    7373
    74 A: Not directly. We have a ticket about that one (#467, #302), but it's deeper than it looks and we haven't come to a conclusion on how to
     74A: Not directly. We have [wiki:ServerSelection a wiki page] and some tickets (linked from the wiki page) about this but it's deeper than it looks and we haven't come to a conclusion on how to
    7575build it.
    7676
    77 The current system will try to distribute the shares as widely as possible, using a different pseudo-random permutation for each file, but
    78 it is completely unaware of server properties like "location". If you have more free servers than shares, it will only put one share on any
    79 given server, but you might wind up with more shares in one location
    80 than the others.
     77The current system will try to distribute the shares as widely as possible, using a different pseudo-random permutation for each file, but it is completely unaware of server properties like "location". If you have more free servers than shares, it will only put one share on any given server, but you might wind up with more shares in one location than the others.
    8178
    82 For example, if you have 15 servers in three locations A:1/2/3/4/5, B:6/7/8/9/10, C:11/12/13/14/15, and use the default {{{3-of-10}}} encoding,
    83 your worst case is winding up with shares on 1/2/3/4/5/6/7/8/9/10, and not use location C at all. The most *likely* case is that you'll wind up
    84 with 3 or 4 shares in each location, but there's nothing in the system to enforce that: it's just shuffling all the servers into a ring,
    85 starting at 0, and assigning shares to servers around and around the ring until all the shares have a home.
     79For example, if you have 15 servers in three locations A:1/2/3/4/5, B:6/7/8/9/10, C:11/12/13/14/15, and use the default {{{3-of-10}}} encoding, your worst case is winding up with shares on 1/2/3/4/5/6/7/8/9/10, and not use location C at all. The most *likely* case is that you'll wind up with 3 or 4 shares in each location, but there's nothing in the system to enforce that: it's just shuffling all the servers into a ring, starting at 0, and assigning shares to servers around and around the ring until all the shares have a home.
    8680
    8781The possible distributions of shares into locations (A, B, C) are: