question Re: Balancing Blocks Between Disks on Datanode in Archives of Support Questions (Read Only)

Balancing Blocks Between Disks on Datanode

transient1 — Tue, 18 Oct 2016 14:03:11 GMT

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.

Re: Balancing Blocks Between Disks on Datanode

weichiu — Tue, 18 Oct 2016 18:08:28 GMT

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-hadoop/

Re: Balancing Blocks Between Disks on Datanode

transient1 — Thu, 20 Oct 2016 14:03:44 GMT

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.

Re: Balancing Blocks Between Disks on Datanode

MSharma — Wed, 05 Apr 2017 22:38:48 GMT

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

Re: Balancing Blocks Between Disks on Datanode

weichiu — Thu, 06 Apr 2017 14:10:06 GMT

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