Re: [nfsv4] FW: New Version Notification for draft-faibish-nfsv4-pnfs-block-disk-protection-01.txt

[<[e-mail]>]

> > > Finally, if there exist two block pNFS implementations, wouldn’t there
> > > be a desire (potentially) to have a different GUID value for each?
> >
> > No.  The goal is to have a single GUID that can be used by all pNFS block
> > implementations to enable operating systems to prevent non-pNFS access to
> > devices used for block pNFS data.  Actual claiming of a pNFS block device
> > for use with a particular implementation happens via the pNFS protocol,
> > but that can't be used early in an OS boot sequence.
> 
> The pNFS block client won't differentiate but the pNFS block MDS may, right?

Not based on the GPT using this GUID.  The MDS is free to add another GUID to
the GPT for other purposes, but checking for a superblock for the MDS's physical
filesystem layout is a more likely mechanism.

> The MDS will certainly scan available devices and determine which are
> within its purview.  It is then assumed that all will have the same GUID
> and that additional information beyond the GPT/GUID will identify
> implementation type and then file system structure.  It then is assumed
> that this is left as an exercise to the MDS server implementation?

Yes - it already works this way today, although the MDS scan will typically not
see block devices that aren't supposed to be used by the MDS.

> That is all fine; a brief summary of that would be helpful in the I-D.
> 
> BTW: if there is only one GUID, then the "SHOULD" in the I-D should
> be a "MUST"?

"SHOULD" was used because it's up to implementers to decide whether to implement
this. The requirement could be rephrased as a conditional "MUST" - if the
implementation uses GPT access protection of pNFS block devices, then this GUID
MUST be used.

Thanks,
--David
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David L. Black, Distinguished Engineer
EMC Corporation, 176 South St., Hopkinton, MA  01748
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