esxi7.0默认的虚拟闪存大小是100多G，对于单硬盘的服务器而言太大了，从esxi 7.0b 开始，可以使用systemMediaSize来调整虚拟闪存，需要注意的是得安装的时候调整，安装完毕以后似乎就不能调整了

Entering the boot option at boot media startup:
Start the host with the install image and when the ESXi installer window appears, press Shift+O within 5 seconds to edit the boot options.
For example, add the following prompt:
systemMediaSize=min

With ESXi 7.0 Update 1c, you can use the installer boot option systemMediaSize to limit the size of system storage partitions on the boot media. If your system has a small footprint that does not require the maximum 138 GB system-storage size, you can limit it to the minimum of 33 GB. The systemMediaSize parameter accepts the following values:

min (33 GB, for single disk or embedded servers)
small (69 GB, for servers with at least 512 GB RAM)
default (138 GB)
max (consume all available space, for multi-terabyte servers)