What are supported upgrade paths to Silva-1.5.6

Dear Developers,


I suppose the answer should come best from the product developers 
(Infrae), but it might be of interest to others as well, so I post the 
question here.

Having a couple of very large sites, mass hosting with hundreds of 
virtual sites on Silva we are in the process of upgrading to Silva-1.5.6 
  right now. Prerequisite for the upgrade is also a change to Zope-2.8.8 
in the application server version, combined with a change in the version 
of ZODB as well.

Now, what is the supported upgrade path?
Is it Zope Export/Import only?
Or can we take the ZODB from a Silva-1.1.5 and copy it to a fresh 
install of Zope-2.8.8 and run the upgrade scripts? Does it matter, that 
the old Data.fs belongs to a ZODB of lower version than the ZODB 
software in Zope-2.8.8 in that case?
Are there other possible ways?
What is supported officially?


Thanks for recommendations,
Reinhard

-- 
Reinhard Hess
Email: [email protected]
Phone: +41-(0)44-632 30 86
Fax:   +41-(0)44-632 13 12
ETH Zuerich
Informatikdienste Technologie- und Informationsmanagement
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CH-8092 Zuerich