rsync - Nov 2008 - Write only changed blocks to disk using rsync client only

I understand that if you want to only transfer changed blocks across the
network that the remote machine must be running rsync server and the local
machine must be running rsync client.  What if I don't care what gets
transferred over the network, I just care what gets written to disk (i.e.
only changed blocks)?  Is there an option to do that in rsync without
needing an rsync server on the other end?

I have an OpenSolaris server that I'm using for backups.  It's running
ZFS,
so if only part of a file changes, I can take a snapshot and be able to have
access to both copies of the file but only store the differences.  However,
if the entire file gets copied back down to disk, ZFS isn't smart enough to
realize that the new blocks copied to disk are the same as the ones that
just got overwritten - so it marks all blocks of the file as changed and
doesn't provide any space-savings.  If rsync had a mode that made sure only
to write to disk the blocks that changed, this would get me around this
problem.  Also, since many of the computers I'll be backing up are Windows
machines, I don't want to hog their CPU, and I don't care how much data
gets
transferred over the network, I'd rather avoid installing the rsync server
on those machines.
-- 
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On 24.11.2008 07:10, bjquinn wrote:
> 
> I understand that if you want to only transfer changed blocks across the
> network that the remote machine must be running rsync server and the local
> machine must be running rsync client.  What if I don't care what gets
> transferred over the network, I just care what gets written to disk (i.e.
> only changed blocks)?  Is there an option to do that in rsync without
> needing an rsync server on the other end?
> 
> I have an OpenSolaris server that I'm using for backups.  It's
running ZFS,
> so if only part of a file changes, I can take a snapshot and be able to
have
> access to both copies of the file but only store the differences.  However,
> if the entire file gets copied back down to disk, ZFS isn't smart
enough to
> realize that the new blocks copied to disk are the same as the ones that
> just got overwritten - so it marks all blocks of the file as changed and
> doesn't provide any space-savings.  If rsync had a mode that made sure
only
> to write to disk the blocks that changed, this would get me around this
> problem.  Also, since many of the computers I'll be backing up are
Windows
> machines, I don't want to hog their CPU, and I don't care how much
data gets
> transferred over the network, I'd rather avoid installing the rsync
server
> on those machines.
--inplace
reads like it is what you want.





Bis denn

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Real Programmers consider "what you see is what you get" to be just as
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On Mon, 2008-11-24 at 07:10 -0800, bjquinn wrote: 
> I understand that if you want to only transfer changed blocks across the
> network that the remote machine must be running rsync server and the local
> machine must be running rsync client.  What if I don't care what gets
> transferred over the network, I just care what gets written to disk (i.e.
> only changed blocks)?  Is there an option to do that in rsync without
> needing an rsync server on the other end?
To expand upon Matthias's response:

The main effect of --inplace is to make rsync update each destination
file by rewriting it in place instead of renaming a new file over it.
However, there is a check so that when the delta-transfer algorithm is
enabled, meaning that information about which blocks are unchanged is
available, rsync will skip writing those blocks to disk.  You'll
probably need to enable the delta-transfer algorithm explicitly with
--no-whole-file because rsync disables it by default when the "network
traffic" that would be optimized is local.

Matt