RE: [Xen-users] XCP - GFS - ISCSI

[Dave Scott <Dave.Scott@xxxxxxxxxxxxx>]

Hi Pasi,

[cc:d Julian who is responsible for storage in XCP]

> I haven't looked at the XCP code yet, but are there some special
> patches for
> LVM to make it work in a shared environment on multiple hosts?
> 
> I guess it's not CLVM, since you support snapshots.. so xapi is doing
> some coordination of management commands and making sure only one LVM
> command is issued at a time?

Julian could describe the detail better than me but my high-level understanding 
is:

* xapi nominates one host to be the 'SR master': all LVM metadata-changing 
commands are run here

* all hosts are allowed to map/unmap LVs so the LVM commands were patched to 
make absolutely sure they didn't attempt to change any metadata

* unless you request a special "raw" LV, vhd metadata is added to the LV: this 
is how we handle snapshots
 
> And after making changes to the LVM configuration xapi runs 'vgscan' on
> every host to pick up the changes?

I'll defer to Julian for this one :-)

Cheers,
Dave


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