You can upgrade the RAM on your Server at any time by using the upgrade feature in My Account. When upgrading or downgrading RAM there are a few important considerations. Sometimes customers are unable to view their new RAM because the operating system does not automatically recognise it.

Windows

Upgrades: Windows servers (r2 2008 and later) automatically allow ?Hot-Add? of RAM.
Downgrades: If you remove RAM from your Server you will need to reboot the server for the change to be recognised.

Linux

When you hot add memory in Linux, it may not register in the guest when you run the free or top command. Linux operating systems may require manual intervention to expose the newly added memory in the guest. The process is called setting the memory to online.

RHEL and CentOS

RHEL/CentOS 6 has ACPI hotplug enabled, so it should see the memory automatically. dmesg will show whether the memory has been seen or not. To set the memory online in RHEL and CentOS:

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

SLES OS

To set the memory online in SLES OS:

Note: These instructions work for SLES OS. Other distributions may be different.

To enable acpi_memhotplug, run this command within the SLES virtual machine:

modprobe acpi_memhotplug

Using vSphere Client, edit the virtual machine settings to increase the memory assigned to the virtual machine. For more information, see Increasing the amount of memory assigned to a virtual machine (1004059).
Bring the memory online in /sys/devices/system/memory with the command:

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

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