DRBD Defaults Too Slow For Today's Servers

I was just setting up a new install of two Ubuntu servers with a TB mirrored between them in realtime using DRBD. It occurred to me while I was configuring DRBD that the default settings are way too slow for current hardware.

For instance, if you're going to set up a high-availability cluster no doubt you're going to have a minimum of a Gigabit network connection between the servers and at least use SATA 300 hard drives - probably in a RAID array to get even more throughput.

The default sync speed in DRBD is only 10 Megabytes / second. It's in your best interests, especially on the initial sync, to increase this considerably. At initial setup time you can safely configure this to be as high as your hardware will allow. Check out this article that describes how to go about calculating it.

For instance, initially my setup used 22 MB as the sync speed, but for the initial sync of 1 TB across a Gigabit crossover using SATA 300 drives was going to take almost 10 hours to complete. My hardware config actually lets me push this as high as 68 MB / second, reducing my initial sync time to about 3 3/4 hours, and that's on two systems with no RAID - simply a 1 TB hard drive synced over a crossover cable.

Once the servers are in production, you generally don't want your sync to use more than 30% of your available bus and network bandwidth, otherwise your sync could interfere with application performance, so tweak that setting back down after the initial sync.

Those settings are all in the /etc/drbd.conf file. Look for "rate XXM;"