VMware ESXi partitions layout includes some old FAT partitions used for the two bootbanks. A strange choice that can bring, in some cases, the corruption of those partitions and you may notice during an upgrade.

With vSphere 8.0 the suggested update procedure is using the images instead of the (old) baselines.

But during a compliance check you may have a critial error like:

A problem with one or more vFAT bootbank partitions was detected. Please refer to KB 91136 and run dosfsck on bootbank partitions.

This problem happen when there was a corrupted vFAT partitions from ESXi 6.5/6.7 environment, that was upgrades to ESXi 7.0.x or ESXi 8.0. This is a known issue and currently there is no resolution.

Each ESXi host has four vFAT partitions on ESXi 6.5 and ESXi 6.7: 2 Bootbanks, Scratch, and Locker. On ESXi 7 and ESXi 8 there are ony two vFAT partitions for the two Bootbanks.

Before do anything I suggest to put the affected host in maintenance mode!

You can show the list of the partition and their type with this command:

esxcli storage filesystem list

Then you need the convert the mount point in a list of disk and partition id:

In this example mpx.vmhba32:C0:T0:L0:5 is first bootbank and mpx.vmhba32:C0:T0:L0:6 is the second.

1. Stop crond, which periodically schedules backup.sh, updating the active bootbank
   kill $(cat /var/run/crond.pid)
2. Only for ESXi 6.x: Stop vmsyslogd, which has open file handles on /scratch (log files)
   /usr/lib/vmware/vmsyslog/bin/shutdown.sh
3. Only for ESXi 6.x: Check for further daemons having open file handles on the scratch partition and stop these daemons
   lsof |grep scratch

For all identifies vFAT partitions, check the file system integrity and repair the disk as needed.

Check the health of the vFAT partition using this command (on the proper partition):

dosfsck -Vv /dev/disks/mpx.vmhba32:C0:T0:L0:5

In case of some errors, uou may see something similar:

Press 1 key twice to confirm the repair and write the changes on the partition.

If the error remain, use the following command (on the proper partition)

dosfsck -a -w /dev/disks/mpx.vmhba32:C0:T0:L0:5

Repeat for each partition.

Reboot the ESXi host, after you have checked and repaired all vFAT partitions.