3:29 a.m.
I suspect the answer is no, as the very idea makes
my head hurt, but a confirmation would be nice:
Am I correct in assuming that it is a very bad idea
to mount a physical disk on both the physical machine
and on a hosted VM at the same time?
I can imagine getting away with it if one were RO, but
not otherwise.
Any takers?
4:14 a.m.
On Fri, Feb 04, 2011 at 04:29:35AM -0500, Dale Amon wrote:
I suspect the answer is no, as the very idea makes
my head hurt, but a confirmation would be nice:
Am I correct in assuming that it is a very bad idea
to mount a physical disk on both the physical machine
and on a hosted VM at the same time?
I can imagine getting away with it if one were RO, but
not otherwise.
Even readonly is not safe. If the host OS has a RO mount
and has partial FS metadata cached, then the guest OS
writes to the FS, this might invalidate the host metadata
and potentially confuse the host OS enough that it would
crash if you're unlucky.
If you want safe concurrent mounts then you need a clustered
or network filesystem. You can also use libguestfs for readonly
access to live guest disks (still has the potential problem I
mention above, but libguestfs runs in a VM so it avoids any
risk to your host OS)
Daniel
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7:57 a.m.
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It is okay to do concurrent mounts if _all_ of the mounts are RO, right?
I frequently have many VM's mounting the same DVD iso (RO, of course).
Should I be anticipating disaster?
David King
Goshen College ITS
davidwk(a)goshen.edu
574-535-7726
On 02/04/2011 05:14 AM, Daniel P. Berrange wrote:
On Fri, Feb 04, 2011 at 04:29:35AM -0500, Dale Amon wrote:
> I suspect the answer is no, as the very idea makes
> my head hurt, but a confirmation would be nice:
>
> Am I correct in assuming that it is a very bad idea
> to mount a physical disk on both the physical machine
> and on a hosted VM at the same time?
>
> I can imagine getting away with it if one were RO, but
> not otherwise.
Even readonly is not safe. If the host OS has a RO mount
and has partial FS metadata cached, then the guest OS
writes to the FS, this might invalidate the host metadata
and potentially confuse the host OS enough that it would
crash if you're unlucky.
If you want safe concurrent mounts then you need a clustered
or network filesystem. You can also use libguestfs for readonly
access to live guest disks (still has the potential problem I
mention above, but libguestfs runs in a VM so it avoids any
risk to your host OS)
Daniel
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David W King