Boniforti Flavio <flavio <at> piramide.ch> writes:

> 
> Hello to both of you, Adam and Andrew.
> 
> > Great suggestion, backing up the VM's as if they were normal 
> > clients...
> 
> That's an option I can't afford to implement. I've been asked
> *explicitly" to backup the images itselves!
> 
...
> 
> Indeed, the splitting would be OK, but still: I'm in need of backing up
> a *big file* which may change in some bytes...

Hi Flavio - I'm developing a "push" backup program, HashBackup, that will backup
a VM image at around 20MB/sec for changed data and 40-50MB/sec for unchanged
data using dedup.  This is on a Macbook 60MB/sec hard drive.  You could attach a
USB disk, backup to that, and also send the incrementals offsite.  Incrementals
will be minimized to the actual disk blocks that changed.

Rsync usually doesn't work that well with VM images because by default it uses a
block size of sqrt(filesize).  For large VM images, the block size becomes very
large.  VM images often have lots of scattered small changes, defeating rsync's
delta algorithm.

In contrast, HashBackup uses 4K blocks for VM images, which minimizes the size
of the incremental.  You could also do this with rsync by specifying the block
size, and I think BackupPC may force a block size of 2K (sometimes?), but rsync
doesn't have efficient data structures for handling this with huge VM image and
just goes CPU bound.

If you want to try it, the beta site is http://www.hashbackup.com

Basically, you would do:

$ hb init -c /mnt/usbdrive/vm1
$ hb backup -c /mnt/usbdrive/vm1 -D1g ~/Documents/VMImages/vm1

Using 1gb of RAM, HashBackup can dedup a 128GB VM image.

Jim


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