Hmm, I would suggest that you re-install vSphere. Is the volume part of a RAID set? Does it only contain the ESXi installation? If so you could delete the RAID volume and start from scratch. Don't know what else you can do here really...
I've seen this before on hosts that boot from SD where the SD card required reformatting, but never on a physical HDD...
Cheers,
Ben Loveday