Disk size Calculation

Products

• DX Unified Infrastructure Management (Nimsoft / UIM)

Issue/Introduction

How disk size is calculated by CDM probe in both windows and Linux?

Environment

Release: DX UIM 23.4*

Component: CDM

OS: Windows/Linux

Resolution

Windows:

CDM probe pull the allocated size of each disk from the server. For total disk size can sum up all the allocated disk sizes.

 

 Linux:

CDM probe uses Linux provided APIs to get the filesystem information which is comparable to df -h command output .

The difference between lsblk and df command outputs and their usage as below.

• lsblk reports the physical disk size:  The lsblk command shows the actual size of the physical disk ( sda in your case, which is 300G). It also shows the partitions on that disk ( sda1 , sda2 , sda3 ).
   
• df -h reports the size of mounted filesystems: The df -h command shows the disk space used and available on mounted filesystems.
• tmpfs is virtual memory: Notice the tmpfs entries in your df -h output. These are temporary file systems that reside in your system's virtual memory (RAM), not on the physical disk. They contribute to the overall disk space usage reported by df -h , but they don't take up space on your /dev/sda disk. tmpfs filesystems are temporary, and their contents are lost when the system is restarted or the filesystem is unmounted.
   
• Partitions might not use the entire disk: It's possible that not all of the 300G disk is allocated to the partitions you see mounted. There might be unpartitioned space or space reserved for other purposes.

CDM provides the list of all the mounted file systems and different metrics for total size, used and free disk size for each filesystem as per standard. It depends on user how they want to monitor the each filesystem.

There is no direct way that CDM provide for calculation of total physical disk size of the VM which is provided by lsblk which just list block devices.