[DRBD-user] Does DRDB do 'intelligent' mirroring?

Steve Purkis steve.purkis at multimap.com
Fri Sep 17 15:22:15 CEST 2004

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.

Hi list,

I'm new to DRDB - in fact I'm just downloading it to give it a run on 
2.4.27 at the mo.  I've got a question that still is unclear to me 
after reading through the docs on drdb.org; it may be a stupid 
question; apologies if it's already been asked (I googled but couldn't 
find anything):

	How does DRDB do mirroring?

I realize the site says that "you could see it as a network raid-1".  I 
guess my question is a bit more specific: does that mean it really does 
the same job that md does?  Or does drdb try and sync only blocks that 
are out of sync (as Peter Breuer's "Fast RAID-1" does).  Or does it do 
something else?  So I guess I could rephrase the question:

	Does DRDB do anything to try and avoid re-syncing an entire device to 
the remote machine?

In the long run, I'm thinking of the scenario where, in a Linux-HA 
cluster, the primary goes down, services failover to the secondary, and 
then the original primary comes back up.  At this point, it makes sense 
to only sync the differences between the two drives to avoid sending 
potentially gigabytes of data over the net.

I guess the next question is:

	If DRDB doesn't do any 'intelligent' resync, are there any plans to?

If not, then is it safe to assume the ideal setup is with a dedicated 
gigabit ethernet link between the 2 boxes, and to carefully select what 
you mirror?

Ta in advance,

More information about the drbd-user mailing list