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Re: [Qemu-devel] [PATCH 1/5] RFC: Efficient VM backup for qemu (v1)


From: Dietmar Maurer
Subject: Re: [Qemu-devel] [PATCH 1/5] RFC: Efficient VM backup for qemu (v1)
Date: Thu, 22 Nov 2012 12:00:26 +0000

> It is a stream of compressed "grains" (data).  They are out-of-order and each
> grain comes with the virtual disk lba where the data should be visible to the
> guest.
> 
> The stream also contains "grain tables" and "grain directories".  This
> metadata makes random read access to the file possible once you have
> downloaded the entire file (i.e. it is seekable).  Although tools can choose 
> to
> consume the stream in sequential order too and ignore the metadata.
> 
> In other words, the format is an out-of-order stream of data chunks plus
> random access lookup tables at the end.
> 
> QEMU's block/vmdk.c already has some support for this format although I
> don't think we generate out-of-order yet.
> 
> The benefit of reusing this code is that existing tools can consume these 
> files.

Compression format is hardcoded to RFC 1951 (defalte). I think this is a major 
disadvantage, 
because it is really slow (compared to lzop).




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