HI @Sadique1 There is no specific option to decommission a disk from Datanode. The best option would be to decommission the Datanode followed by removing the disk and recommission it back.
https://community.cloudera.com/t5/Community-Articles/Decommission-and-Reconfigure-Data-Node-Disks/ta-p/248262
The downside of decommission and recommission is that it will need to copy all the blocks to another host for all disks, not just the one you are removing.
OR
Considering that you don't have files with rep factor=1(fsck will tell you if any such files exist.), You could remove the disk from 1 DN and restart it, and wait for the NN to recover the under replicated blocks. Then repeat for each node.
Note : If there are files with rep factor as 1 on those Datanode disks, then you will be getting missing blocks.
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