Recently when working with a very old, decrepit server that was running out of disk space I went to compress a folder of logs in NTFS and the compress box was greyed out and I was unable to compress it.
This is because in NTFS the compression attribute isn’t supported for volumes with cluster sizes larger than 4k — this happened to be sized at 64k thus the inability.
The way that I typically check this is by simply running “CHKDSK D:” replacing D: with your prospective drive letter. The output of this will display your cluster size in bytes (divide by 1024 to get the cluster size in kb)
Hope I’ve made your day a little bit easier!