Slow SSD perfomance with ESXi 6.5 and older AHCI controllers

ESXi 6.5 includes a new native driver (vmw_ahci) for SATA AHCI controllers, but that introduces performance problems with a lot of controllers and/or disks.

Try to disable the native driver and revert to the older sata-ahci driver by running

 esxcli system module set --enabled=false --module=vmw_ahci

Reboot the server after changing it and your performance should be OK again.