dan wrote:

> just want to clarify here.
> 
> you have x number of remote hosts, all running the same OS and presumably
> have almost identical files (size, permissions etc)? and you want back one
> up and then clone that backup for each of the other machines to avoid
> transfering the data numerous times?
> 
> you should add the -H flag to cp or rsync to take hardlinks with:
> 
> rsync -aH /var/lib/backuppc/pc/host1/0 /var/lib/backuppc/pc/host2/0
> cp -aH /var/lib/backuppc/pc/host1/0 /var/lib/backuppc/pc/host2/0
> 
> This should help you reduce the initial transfer cost in bandwidth but the
> remote systems wont have the same mtime so you wont be able to keep just
> one copy of the file on the backuppc server hardlinked across all of the
> similar
> hosts AFAIK.  rsync will only want to change the timestamp but will create
> a new file in the pool because the files are not identical because the
> times are different.
> 
> someone please correct me if this is incorrect.  will rsync run an md4 on
> the file and consider it identical reguardless of the time?
> 
> As a workaround, you might make a list of files on the template system
> including mtime and then write a script to crawl through each of the other
> machines filesystems and use touch to alter the mtime to match the first
> machine.  That way rsync will see them as identical.  Generally speaking,
> if the machine times are the same, altering the mtime of the files wouldnt
> have any adverse effects.
> 
> good luck!
> 
I would believe the pooling scheme of backuppc did not duplicate a file
because his attributes are different. If I'm wrong, I can not believe that
the example from the documentation can be true:
----------------------------
Here's one real example for an environment that is backing up 65 laptops
with compression off. Each full backup averages 3.2GB. Each incremental
backup averages about 0.2GB. Storing one full backup and two incremental
backups per laptop is around 240GB of raw data. But because of the pooling
of identical files, only 87GB is used. This is without compression.
----------------------------

But independent from that - my goal is to reduce bandwith usage through
rsync. And rsync will not send data which is already on the receiver side.

Thanks for the -H hint. But I do not fully understand. The cp documentation
says:  "follow command-line symbolic links in SOURCE". I would believe that
files, which are reachable through symbolic links, are also copied if -H is
present. Is that true?
I thought that cp will copy hardlinks by default as hardlinks if source and
destination are on the same device.

br
Matthias
-- 
Don't Panic


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