One of the RAM disk that make up the ESXi host root file system might reach its resource pool limit as a result of a software failure or an accidental use of an incorrect path.
Example
When an administrator manually copies files to the host and accidentally uses an incorrect path (that is, one outside /vmfs/volumes), the following error message appears:
The ramdisk 'root' is full. As a result, the file /testfile could not be written.
In the /var/log/vmkernel.log file, the following message may also appear.
VisorFSRam: 233: Cannot extend visorfs file /var/lib/vmware/hostd/journal/ because its ramdisk (root) is full.
Impact
Files on the affected RAM disk can no longer be extended.
Various administrative actions depend on the ability to write files to various parts of the root file system and may fail if a RAM disk is full.
Identify files in the root directory larger than 1 MB:
find / -size +1024k -exec du -h {} \; | less
Old/stale left over ESXi host log bundles should be copied/moved off and removed to provide space back to the ESXi host
If the error was caused by an administrator action, delete the files that use the incorrect path or move them to a datastore. Otherwise, contact VMware Support.