HDFS Distribution by adding HDD's to a SSD-only cluster without storage policies

[#1]

Hey together, 

we're running a CDP Private Cloud Base Cluster with actually 6 Nodes. All 6 Nodes running fully on SSD storage. I found out that HDFS thinks the SSDs are normal disk, because it is not configured as SSD storage like this --> "[SSD]/grid/n/dn", actually its "/grid/n/dn". Now we're planning to add four other servers from an older cluster with normal disks.

My action plan is as follows: 

1. configure existing storage/server to SSD -> "[SSD]/grid/n/dn"
2. add the other four server an configure it -> "[DISK]/grid/n/dn"

3. restart recommended services

I've got the following questions: 

- Will HDFS distribute the blocks across all nodes (SSD and disk?) without any storage policy configured? So that we have a homogeneous storage. 

- How will services react to this changes in storage, for example HBase?

- If we configure a homogeneous storage, as i described: does reconfiguring the storage paths of the Datanodes to SSDs add any value/benefit at all?

Thanks for your help!

Regards, 

Timo

[#2 · Accepted solution]

We added the new machines and configured it to all Disk. Working fine so far.