In case you do not have access to above, here is some snippet that may help:
In order to understand the difference, we need to know about how df and Cloudera Manager calculate the disk usage.
df output: From the df output, if you sum the space used and the free space, it does not add up to the total space on the disk. The reason for this is that the actual usable space on the disk is not the same as the disk capacity, as there is overhead and space reserved by the OS. Please see this article "Why The Linux df Command Shows Lesser Free Disk Space?" for more detail information. The way df calculates the %used does not take account of this and it makes it look like there is more % free than there really is.
Cloudera Manager host metrics: The way Cloudera Manager calculates the used space is to take the 'usable free space' report by df (ie 931G) and subtract that from the total disk capacity (985G), which is what you see here. In other words, CM includes the unusable / reserved overhead on the disk in the used space, while the OS does not.
You may want to check if the 'space remaining' on each is approximately the same. If so, then there should be no concerns because the space used is generally different due to Cloudera Manager UI includes the overhead while df does not.
Li Wang, Technical Solution Manager
Was your question answered? Make sure to mark the answer as the accepted solution. If you find a reply useful, say thanks by clicking on the thumbs up button.