[DRBD-user] Replication for disaster recovery

Digimer lists at alteeve.ca
Fri Apr 25 19:22:00 CEST 2014

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

On 25/04/14 05:06 AM, Velko wrote:
> Hello,
> I'm planing to use DRBD for DR and since I've never used it, I have a
> few questions.
> 1. Have anyone used it for replication to different data center (both
> east coast of USA)? I was thinking of using protocol A without DRBD
> proxy (maybe protocol B). How does it work in real life?

You would want Protocol A, or else your storage performance would 
effectively drop to the same speed as the network. Of course, the 
trade-off is that the remote side will often be a little behind 
production (or a lot behind, depending of how much data is being written 
compared to the network speed).

> 2. Since there is a lot of 2-3 MB files in size of 1GB daily that are
> not that important in case I need to switch to secondary site, would it
> be possible to put those files on separate partition (DRBD device) and
> configure it to have lower priority? Maybe only periodicaly
> resynchronization? I understood that it is much more efficient.
> Partition with less changing files and InnoDB tables would have high
> priority.

Not easily. I suppose you could create a separate resource which would 
use a different port and then try QoS, but that could get tricky (in 
general, not DRBD specific, QoS can be a pita).

> 3. Would having separate NIC for replications improve performances in
> this case?

Depends entirely on where your bottle-neck is. I suspect that will be 
your WAN connection, which you didn't talk about. ;)

> 4. Is it possible to configure DRBD to automatically demote in case of
> loosing internet connection?

Not safely, no. There is now reliable way to use fencing, and without 
reliable fencing, only a human can ensure the state of the lost node. To 
try and automate it would very likely lead to split-brains.

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