Todd Lipcon has posted comments on this change.

Change subject: KUDU-1952 Improve block placement
......................................................................


Patch Set 1:

(3 comments)

Just took a quick look at the commit message and new configs, not too much on 
the code structure, since Adar said he'd be reviewing the code.

http://gerrit.cloudera.org:8080/#/c/6636/1//COMMIT_MSG
Commit Message:

Line 10: single-disk failure. Throughout the code, the term "DataDir" refers to
would be good to link to the design doc somewhere here


PS1, Line 14: This patch adds a mapping from tablet to a set of disks and uses 
it to
            : replace the existing round-robin placement of blocks. Tablets are
            : m
it would be good in the commit message to explain the impact of this patch.

With just this patch, and no follow-up work, is there a negative impact here? 
e.g. are we now limiting tablets to 3 disks, but still not actually able to 
recover from a wider variety of failures? If so, we should probably have a flag 
to disable the new behavior so that our trunk remains non-regressive from the 
most recent release.

Also curious about upgrade impact here.


http://gerrit.cloudera.org:8080/#/c/6636/1/src/kudu/fs/data_dirs.cc
File src/kudu/fs/data_dirs.cc:

Line 57:               "Indicates the target number of data dirs to spread each 
"
what's the behavior here if the configuration is larger than the number of data 
dirs?

Similar to one of my top-level comments on the commit message: I'm afraid this 
is currently adding additional placement restrictions but not achieving the 
recovery benefits, so we should probably have this off for now


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Gerrit-MessageType: comment
Gerrit-Change-Id: I9828147f4fa5c4d7f6ed23441dca5a116b8cb11b
Gerrit-PatchSet: 1
Gerrit-Project: kudu
Gerrit-Branch: master
Gerrit-Owner: Andrew Wong <[email protected]>
Gerrit-Reviewer: Adar Dembo <[email protected]>
Gerrit-Reviewer: David Ribeiro Alves <[email protected]>
Gerrit-Reviewer: Jean-Daniel Cryans <[email protected]>
Gerrit-Reviewer: Kudu Jenkins
Gerrit-Reviewer: Tidy Bot
Gerrit-Reviewer: Todd Lipcon <[email protected]>
Gerrit-HasComments: Yes

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