tahoe-lafs/tahoe-lafs
tahoe-lafs
/
tahoe-lafs
2
0
Fork 0
Code Issues Pull Requests 23 Packages Projects Releases 1 Wiki Activity

Note that servers of happiness only applies to immutable files for the moment

This commit is contained in:
Kevan Carstensen 2010-05-23 21:28:36 -07:00
parent 4141d95588
commit a0a770a96a
2 changed files with 27 additions and 13 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

27
docs/architecture.txt
View File

@ -195,17 +195,28 @@ that information to the share-to-server table. This lets us do less work for
files which have been uploaded once before, while making sure we still wind up files which have been uploaded once before, while making sure we still wind up
with as many shares as we desire. with as many shares as we desire.
If we are unable to place every share that we want, but we still managed to Before a file upload is called successful, it has to pass an upload health
place enough shares on enough servers to achieve a condition called "servers of check. For immutable files, we check to see that a condition called
happiness" then we'll do the upload anyways. If we cannot achieve "servers of 'servers-of-happiness' is satisfied. When satisfied, 'servers-of-happiness'
happiness", the upload is declared a failure. assures us that enough pieces of the file are distributed across enough
servers on the grid to ensure that the availability of the file will not be
affected if a few of those servers later fail. For mutable files and
directories, we check to see that all of the encoded shares generated during
the upload process were successfully placed on the grid. This is a weaker
check than 'servers-of-happiness'; it does not consider any information about
how the encoded shares are placed on the grid, and cannot detect situations in
which all or a majority of the encoded shares generated during the upload
process reside on only one storage server. We hope to extend
'servers-of-happiness' to mutable files in a future release of Tahoe-LAFS. If,
at the end of the upload process, the appropriate upload health check fails,
the upload is considered a failure.
The current defaults use k=3, servers_of_happiness=7, and N=10. N=10 means that The current defaults use k=3, servers_of_happiness=7, and N=10. N=10 means that
we'll try to place 10 shares. k=3 means that we need any three shares to we'll try to place 10 shares. k=3 means that we need any three shares to
recover the file. servers_of_happiness=7 means that we'll consider the upload recover the file. servers_of_happiness=7 means that we'll consider an immutable
to be successful if we can place shares on enough servers that there are 7 file upload to be successful if we can place shares on enough servers that
different servers, the correct functioning of any k of which guarantee the there are 7 different servers, the correct functioning of any k of which
availability of the file. guarantee the availability of the immutable file.
N=10 and k=3 means there is a 3.3x expansion factor. On a small grid, you N=10 and k=3 means there is a 3.3x expansion factor. On a small grid, you
should set N about equal to the number of storage servers in your grid; on a should set N about equal to the number of storage servers in your grid; on a

13
docs/configuration.txt
View File

@ -272,11 +272,14 @@ shares.happy = (int, optional) k <= happy <= N
larger than 256, because of the 8-bit erasure-coding algorithm that Tahoe larger than 256, because of the 8-bit erasure-coding algorithm that Tahoe
uses. uses.
shares.happy allows you control over the distribution of your file. An upload shares.happy allows you control over the distribution of your immutable file.
is only considered successful if shares are placed on at least 'shares.happy' An upload is only considered successful if shares are placed on at least
distinct servers, the correct functioning of at least k of which is sufficient 'shares.happy' distinct servers, the correct functioning of at least k of
to guarantee the availability of the uploaded file. This value should not be which is sufficient to guarantee the availability of the uploaded file. This
larger than the number of servers on your grid. value should not be larger than the number of servers on your grid.
(Mutable files use a different share placement algorithm that does not
consider this parameter.)
== Storage Server Configuration == == Storage Server Configuration ==