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Re: [Xen-users] Disks shared by default ?

The documentation for this should probably be updated. http://wiki.xen.org/wiki/XL_vs_Xend_Feature_Comparison says that the "w!" notation is not supported by XL, but it doesn't mention that sharing is implied by default. The footnote has a link to http://wiki.xen.org/wiki/XL#Anti-Features which doesn't even mention anything about sharing which makes the footnote irrelevant. And there doesn't appear to be any page which actually talks about disk sharing, where it could be noted that sharing is only supported on "phy:" disks and not image files.

There is also no documentation about what disk sharing is actually useful for. E.g. which filesystems would even support concurrent access to the underlying block device like this, and what mount options would be necessary?

Quoting Sébastien Chaumat <sebastien.chaumat@xxxxxxxx>:

Found it :
 nearly 3 yrs old

On 10 May 2016 at 20:11, Sarah Newman <srn@xxxxxxxxx> wrote:

On 05/10/2016 03:24 AM, Sébastien Chaumat wrote:
> Hello,
>  I just realized that in recent xen version (xl stack)  phy: disks are
> shared by default between domUs:
> eg:
> disk        = [ '/dev/VGdomU/test-ext4,raw,xvda2,w' ]
> can be used in multiple simultaneous domUs without a warning (learned the
> hard way).
> When this the change from 'w!' syntax to simple 'w' for shared disk
>  occured ? what was the rationale for it ?
> I could not find this information.
> Is there any option to forbid sharing vbd accross domU by default ?

If you find out, please post back.


Sébastien CHAUMAT
Open source IT Architect

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