I am relatively new to ESX. This message is primarily for users fresh to ESXi like me
A. Your computer supports Hard Disk in ATA/AHCI mode properly. I tested this on Dell Optiplex, I am not sure how it will work on other computer/motherboards.
B. You are running earlier version and try to upgrade to ESX 3.5i Update 4.
1. The information is summarized from all sources so credits goto all of them
2. Some users will ask you to use USB stick for ESXi. In my case, I am not.
3. Prior to Update4, many test users choose ATA configuration for cheapest setup.
4. After ESX 3.5i Update 4 is applied and reboot. PANIC cannot find disk partition.
5. The main reason is AHCI is now activated.
6. So the exact procedure that works for me are
6a. Applied ESX 3.5i Update 4 patch.
6b. Reboot, immediately goto computer BIOS SATA MODE configuration. Change from ATA to AHCI. Save change, reboot again.
6c. In my case, now it is booting again normally.
6d. In case you can boot normally but cannot see the datastore easily, can use the LVM resig option suggested by member in this forum a few days ago.
7. In case you missed the steps earlier and the damaged is done, follow the steps below
7a. Upon ESXi boot screen, press Shift-R and load the old-firmware (previously working)
7b. Use VI Update software to update the firmware again from (old-working) to newest firmware (update4)
7c. Goto physical ESXi host, shutdown and reboot, immediately goto computer BIOS screen SATA mode configuration, change from ATA to AHCI. save, reboot
7d. ESXi host should now boot again with newest firmware.
7e. In case you can boot normally but cannot see the datastore easily,
can use the LVM resig option suggested by member in this forum a few