On Mon, 11 Mar 2013, Carl Johnson wrote:
Warren Block <wbl...@wonkity.com> writes:
On Mon, 11 Mar 2013, Carl Johnson wrote:
It is my understanding that FreeBSD doesn't allow using part of a disk,
but grabs the entire disk. That means that VirtualBox can't use
partitions on a disk that any other partitions are being used by
anything else, including FreeBSD itself. Am I wrong about this? I use
VirtualBox using vdmk for an entire disk, but I have never been able to
share with anything else.
It's very hard to tell what situation is being described here. If the
VMDK is a pointer to a whole physical disk, that would probably make
the disk only usable by one VM. It should be possible to make the
VMDK point to just one partition on the disk. Then other VMs or a
physical machine could use those other partitions while the FreeBSD VM
was running.
I was thinking of the case where I tried to allow direct access by a
virtual machine to a slice on the same disk that I was running FreeBSD
off of. I just looked further into that and discovered that it is
possible, but not allowed by geom by default. It can be done by setting
'sysctl kern.geom.debugflags=0x10'. I am sure that you are aware of the
dangers, but for anybody else reading this check out the warning in the
geom(4) manpage. They refer to this option as 'allow foot shooting' for
a reason.
That's kind of what I was saying. If you can get the VMDK to refer to
just the one slice/partition that the VM needs, it won't lock the whole
disk. For example, ada0s2a rather than ada0s2. Of course, it would be
bad to share the same partition between more than one VM or physical
machine at the same time unless it is mounted read-only by all of them.
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