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[Xen-API] XCP: RFC: compressing VM exports by default

To: "xen-api@xxxxxxxxxxxxxxxxxxx" <xen-api@xxxxxxxxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: [Xen-API] XCP: RFC: compressing VM exports by default
From: Dave Scott <Dave.Scott@xxxxxxxxxxxxx>
Date: Tue, 22 Jun 2010 15:08:50 +0100
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Thread-topic: XCP: RFC: 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.

Comments appreciated!


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