Hot Add CPU/Memory/Disk in Linux Virtual Machine

Many out there will be wondering how to dynamically increase the memory/cpu/disk when the System is actually active!!!....it would have been impossible a decade ago....but in this cloud era....it is very much possible....and here is how to....




Hot Adding Memory

To set the memory online in RHEL and CentOS:

Note: These instructions work for RHEL and CentOS. Other distributions may be different.

    Run this command to check the state of the memory, looking for memory that appears offline:

    grep line /sys/devices/system/memory/*/state
 
    If memory appears as offline, set it to online with the command:

    echo online > /sys/devices/system/memory/memory[number]/state

Hot Adding CPU

To check the online CPUs
 
ll /sys/devices/system/cpu/cpuX/online   (where X denotes the number of CPU)

echo 1 > /sys/devices/system/cpu/cpu3/online (here incase the user added the 3rd cpu to the running system)

Hot Adding Disk

    *1st Find the scsi host name from the following directory


    # ls /sys/class/scsi_host

    * Output will be as follows

      host0

    * Now execute the following command to scan the scsi module

    echo "- - -" > /sys/class/scsi_host/host0/scan
    fdisk -l

    tail -f /var/log/message

Hope this helps!!!.....feel free to contact me incase of any assistance!!!