Red Hat Bugzilla – Bug 432394
guest boot device restrictions unclear
Last modified: 2009-08-20 00:02:16 EDT
The virtualization guide states:
"The guest boot device can not be located on a disk using a para-virtualized
block device drivers. However, user data and applications can reside on devices
using the para-virtualized block device driver."
This is terribly unclear—the phrase "user data and applications" really doesn't
*mean* anything, so it doesn't help to clarify what can and cannot be located on
a device using para-virtualized block device drivers.
Does this mean that only the grub boot device cannot be located on a device
using para-virtualized block device drivers? Or does it also mean that the
kernel's root target (i.e., the root=DEVICE line argument to the kernel) cannot
be located on a device using para-virtualized block device drivers?
I suggest that you clarify the restrictions using terms that Linux system
administrators commonly understand: the grub boot device, the kernel root=DEVICE
device, and any other devices/partitions/volumes (e.g., /lib).
We have crafted new guidance documentation for para-virtualized drivers located:
Can you please review and let me know if that answers your questions?
Created attachment 296774 [details]
I've reviewed the new guidance documentation. It doesn't answer my question.
The specific paragraph I complained about is unchanged. As far as I can tell,
the only clarification you added was the following paragraph (at the start of
the step-by-step instructions for each OS):
"These packages do not support booting from a para-virtualized disk. Booting
the guest operating system kernel still requires the use of the emulated IDE
driver, while any other (non-system) user-level application and data disks can
use the para-virtualized block device driver."
Furthermore, the last example in section 8.2 ("8.2. Virtual Storage Devices")
lists examples of para-virtualized block devices that are clearly not part of a
regular OS install (e.g., "/mnt/pvdisk_xvda").
The phrase "user-level application and data disks" is just as meaningless as
"user data and applications".
Based on my technical understanding of how the para-virtualized device drivers
work, I've rewritten the "Important Restrictions" section of Chapter 2. If my
rewrite is technically correct (I think it is, but I'm not certain, which I why
I filed this bug in the first place), please consider using it (or something
similar to it).
(Null comment to toggle state out of NEEDINFO...)
I have edited and updated these changes but the books may not be made public for
a little while. The changes have also been added to the Virtualization Guide for
Red Hat Enterprise Linux 5.2. I will forward you some links after these changes
have been made public.