Balancing Blocks Between Disks on Datanode

[#1]

Hi. Some of my datanodes have different disk size. For example:

/dev/sdc1 918G 384G 534G 42% /data/disk1
/dev/sdd1 459G 381G 78G 84% /data/disk2
/dev/sde1 459G 391G 69G 86% /data/disk3
/dev/sdf1 459G 389G 70G 85% /data/disk4

My understanding is that there is currently no functionality for balancing within a datanode, so I'd have to move data around manually. I've found this article on performing the procedure: http://www-01.ibm.com/support/docview.wss?uid=swg21702775 (Procedure 1). Has anyone actually done this (or something similar)? Can you share any issues/caveats you ran across? Is this the best way to do it? If the other 3 disks fill up, will that datanode continue to write to disk1? 

Thank you. 

[#2 · Accepted solution]

I feel what you described has its own inherent risk.

Since CDH5.8.2, you can use a new HDFS feature: intra datanode balancer to do exactly what you asked for. And we have a new blog post about this feature:

http://blog.cloudera.com/blog/2016/10/how-to-use-the-new-hdfs-intra-datanode-disk-balancer-in-apache...

[#3]

Thank you. This is a great feature, and I appreciate the link. Unfortunately, our cluster is running 5.7.1, and given my lack of experience with CDH (I inherited this cluster) I'm loathe to upgrade it at the moment.

[#4]

Same issue, do we have any such thing for  version older than 5.8 . disk balancer

[#5]

diskbalanacer is a new feature in CDH5.8, and by definition, a new feature will not be backported to an older minor version.