Re: [Xen-API] Configuration needed to share a VDI

[Dave Scott <Dave.Scott@xxxxxxxxxxxxx>]

Hi

Anil wrote:
> On 18 May 2012, at 14:58, Mike McClurg <mike.mcclurg@xxxxxxxxxx> wrote:
> 
> > On 18/05/12 11:49, Carlos Eduardo Tavares Terra wrote:
> >> Do I need to do any special configuration in XCP 1.1 or in the SRs
> to be
> >> capable of sharing a VDI between two virtual machines?
> >> Is it possible to do in XCP?
> >
> > You could possibly do this if only one VM attaches the disk RW, but
> you should definitely not do this if you want more than one of the VMs
> to attach the disk RW. For that, you should use something like NFS
> instead.
> 
> I think Carlos is using a concurrent file system or database, and so
> sharing the RW VBD is fine.
> 
> Isn't this just a case of marking the VBDs as shareable to disable the
> xapi safety check?

As well as marking the VDI as sharable you also have to be careful with .vhds. 
If all the VMs sharing the VDI are on the same host they'd all share the same 
"tapdisk" process and this would be fine. If they were sharing the VDIs across 
hosts then you'd have multiple tapdisk writing the .vhd metadata concurrently 
which would lead to corruption.

If you need to share the VDIs across hosts then try creating a "raw" format 
VDI, using

$ xe vdi-create sr-uuid=... name-label=foo virtual-size=... type=user 
sm-config:type=raw

Cheers,
Dave

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