squito commented on issue #23614: [SPARK-26689][CORE]Support blacklisting bad 
disk directory and retry in DiskBlockManager
URL: https://github.com/apache/spark/pull/23614#issuecomment-458654349
 
 
   oh I see, this is handling a bad disk on the driver, not the executors.  A 
bad disk on the executors should be handled by blacklisting.
   
   In general, spark's fault tolerance for the driver is extremely poor, its a 
single point of failure for lots of reasons.  Still, this may be a small fix to 
improve things somewhat, without any real guarantees.
   
   There are a lot of cases here to think through carefully.  Eg. as noted in 
the comments, this has to be kept in sync w/ 
ExternalShuffleBlockResolver#getFile.  Even if you put in the same logic, its 
still possible they'll end up with different views of the actual bad 
directories.  Also probably want to update getAllFiles() as well to respect the 
badDirs.  And what happens when a dir with lots of data in it is suddenly 
marked as bad, that all other internal state is updated reasonably (maybe not 
immediately, but when it is updated that it makes sense).
   
   I'm just thinking aloud about this change ... still on the fence of whether 
its good or not

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