Even I agree with Abhilash.This is because esx i snot able to recognise the fs.
It seems you are having fat16 filesystem on this lun.
So better delete all the partitions existing in this lun using fdisk command.
Recreate the gpt partition with partedUtil.
The create vmfs on the partition.
Regards,
SatyS
If you find this useful,mark the answer as correct/helpful