Re: [Xen-devel] [PATCH] Blktap: Userspace file-based image support.(RFC)

[Dan Smith <danms@xxxxxxxxxx>]

ST> Could be useful in places, but it introduces a number of new
ST> dependencies.  

I was mostly commenting about making migrating block devices as easy
as (or easier) than file-backed domains, especially from a migration
point of view.  Being able to use local LVMs but still migrate easily
without a NAS would be cool, I think, where appropriate.

ST> The destination host now relies on the source host for data, so if
ST> the source crashes, you crash the destination too;

Sure, which a NAS solves, assuming the NAS is stable.

ST> and if you power-cycle, how do you track where in your cluster the
ST> latest copy of the block device is?

I think that keeping metadata on that and invalidating blocks when you
pull them off the source host could be done without too much trouble.
Plus, I'm not talking about multiple-writers, so I think you could
ignore a lot of the normal locking issues.

ST> A true NAS solution isolates the Xen hosts from these problems.

Absolutely.  So what's the benefit of having image files on NFS (as
you mentioned) if you can use nbd or iSCSI?

-- 
Dan Smith
IBM Linux Technology Center
Open Hypervisor Team
email: danms@xxxxxxxxxx

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