As part of the 2010 Annual Xen.org survey response, I intend to push out more developer related content to the community via this blog…
From: Dave Scott
Re: Compressing VM Exports by Default
In XCP a VM “export” is a serialized VM, including metadata and usually raw disk blocks. The format is a very simple tar file (really stream) with an XML file at the front containing version information and metadata.
Unfortunately VM exports containing raw disk blocks can be very large and their size makes them difficult to store and distribute over the network. I propose to turn on compression by default by filtering the exports through gzip and to auto-detect both compressed and uncompressed exports on import.
I’ve written up my proposal on the wiki:
One implication is that new (compressed) exports will fail to import on older servers. However (a) there’s an easy workaround (gunzip); and (b) I think being able to import an old (uncompressed) export on a new server is more important than the other way around.
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