[CentOS-virt] Not file system fox xbd0 (dev 0x8e00) cannot mount root, error =79

I get the following error does anybody know how to fix it. Thanks,

root device (default xbd0a): ex0 use one of: xbd0[a-p] xennet0 md0[a-p] ddb halt reboot root device (default xbd0a): xbd0a dump device (default xbd0b): xbd0b file system (default generic): generic root on xbd0a dumps on xbd0b mountroot: trying lfs... mountroot: trying ffs... mountroot: trying ext2fs... mountroot: trying nfs... mountroot: trying smbfs... mountroot: trying ntfs... mountroot: trying msdos... mountroot: trying cd9660... mountroot: trying coda... no file system for xbd0 (dev 0x8e00) cannot mount root, error = 79

Thanks, - Augustin