Red Hat Enterprise Linux 6.1 introduced naming scheme adjustments for emulated SCSI disks used with paravirtual drivers to prevent namespace clashes between emulated IDE and emulated SCSI disks. Both emulated disk types use the paravirt block device 'xvd'. Consider the example below:
| 6.0 | 6.1 or later
emulated IDE | hda -> xvda | unchanged
emulated SCSI | sda -> xvda | sda -> xvde, sdb -> xvdf, ...
This update introduces a new module parameter, xen_blkfront.sda_is_xvda, that provides a seamless upgrade path from 6.0 to 6.3 kernel release. The default value of xen_blkfront.sda_is_xvda is 0 and it keeps the naming scheme consistent with 6.1 and later releases. When xen_blkfront.sda_is_xvda is set to 1, the naming scheme reverts to the 6.0-compatible mode.
Note that when upgrading from 6.0 to 6.3 release, if a virtual machine specifies emulated SCSI devices and utilizes paravirtual drivers and uses explicit disk names such as xvd[a-d], it is advised to add the xen_blkfront.sda_is_xvda=1 parameter to the kernel command line before performing the upgrade.