BDsync: Block Device sync

Rolf Fokkens rolf at
Wed Jun 27 09:15:50 MDT 2012

DRBD seems a suitable alternative, but I looked into it and it seemed
quiet complex. I am mostly interrested in asynchronous replication, and
I'm not sure if this works in a proper way. The proper way for me means
that write order is preserved for consistency reasons (explained below),
and I can't figure that out. Apart from that I think I need the buffering
functionality provided by DRBD proxy, which has specific licensing terms.

Although not as efficient as DRBD bdsync is very simple. And I meets my
consistency requirement by applying it on a snapshot of an LVM volume,
which results in a (compressed) diff file that I only apply on the
destination LVM device after completion. So afterwards I always have a
consistent image.

The consistency is important because every LVM image is a disk image for a
virtual machine. By syncing an LVM shapshot I'm sure I'm replicating a
moment in time like someone pulled the power plug. I assume that the VM's
can recover from that.

I do agree though that DRBD may be a suitable alternative.


Op 27-06-12 15:48 schreef Karl O. Pinc <kop at>:

>On 06/27/2012 06:51:29 AM, Rolf Fokkens wrote:
>> After having wrestled with rsync and several patches I found a
>> solution to
>> synchronize block devices: BDsync.
>> Bdsync can be used to synchronize block devices over a network. It
>> generates
>> a "binary diff" in an efficient way by comparing  MD5 checksums of
>> 32k
>> blocks of block devices. This binary diff can be applied to
>> "destination"
>> after which  the local blockdevices are synchronized.
>> Interrested people can download the sources from:
>I'm curious.  Why would use use bdsync instead of drdb?
>Karl <kop at>
>Free Software:  "You don't pay back, you pay forward."
>                 -- Robert A. Heinlein

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