[ESXi] Change ESX-OSData partition size on ESXi 7.0

Changing the ESX-OSData partition size refers to modifying the size of the partition that contains the operating system and other system files for an ESXi (VMware vSphere Hypervisor) host. This partition is typically used for storing the ESXi image, log files, and other system files, and its size can have a direct impact on the overall performance and stability of the ESXi host.

After installing ESXI 7 on Intel NUC, I discovered that the Storage section only shows 104.75 GB of free space, while I am using a 250 GB SSD. Where did the remaining 120 GB of hard drive go?

Checking the partitions again discovered that ESXi took up 128GB for the ESX-OSData partition. In addition, it also takes 8GB more for 2 partitions Boot-bank 0 and Boot-bank 1. So the remaining 100 GB of Datastore is reasonable.

But why does ESXi take up so many hard drives? Is there a way to reduce occupancy to a minimum?

Storage system of the ESXi 7

Me Find out more only to know that this is the default setting of the storage system on ESXi 7.0, as shown in the illustration below.

Depending on the capacity of the hard drive, ESXi 7.0 will automatically divide the partition according to the following table

Boot Media Size 4-10 GB 10-32 GB 32-128 GB >128 GB
System Boot 100 MB 100 MB 100 MB 100 MB
Boot-bank 0 500 MB 1 GB 4 GB 4 GB
Boot-bank 1 500 MB 1 GB 4 GB 4 GB
ESX-OSData remaining space remaining space remaining space up to 128 GB
VMFS datastore       remaining space for media size > 142 GB

The hard drive I am using is larger than 142 GB, so the setting of the outer right column will automatically be applied along with the occupied 128 GB ESX-OSData partition.

With hard drives 1TB and above, 136GB occupied by system partitions is not a big deal. The remaining hard drive is still very much for the virtual machine.

But with small ESXi systems, such as at home, a hard drive of only 250GB that is already occupied by more than half of the system is not good. Only more than 100 GB left to contain the ISO file and save the virtual machine is too limited.

How to reduce the size of the ESX-OSData partition?

Resize ESX-OSData partition

Since update 7.0 Update 1c, ESXi has added optional support systemMediaSize on startup settings to change the default size of the ESX-OSData partition. The parameters are as follows:

  • min (24GB): applies to systems with only 1 hard disk or integrated servers.
  • small (55GB): applies to servers with at least 512GB of RAM.
  • max (uses the entire free space of the hard drive): for super servers.

Note: If you have already installed ESXi 7.0 with default settings, there is no way to reduce the size of the ESX-OSData partition to min 33GB. Must reinstall from scratch.

There are 2 ways to set parameters systemMediaSize when installing ESXi 7.0

Enter parameters when booting from USB

Boot the machine and boot from the ESXi installation USB. When the setting screen appears, hold down Shift+O for 5 seconds, then enter the corresponding setting. For example: systemMediaSize=small

Edit boot.cfg directly

If you don’t want to enter parameters at startup, you can edit the file boot.cfg located in the installation USB. Plug the USB into another computer, open the file boot.cfg and add parameters systemMediaSize=min at the end of the line kernelopt

For example, after editing it will look like this: kernelopt=runweasel systemMediaSize=min

After reinstalling ESXi 7.0 with parameters systemMediaSize=minVMFSL has been reduced to 23.9 GB, and the VMFS partition for the datastore has increased to 200.88GB, with more free space available for virtual machines.

Source: VMWare Docs, VMWare KB

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