I’m speaking at Percona Live, LinuxCon Europe, and linux.conf.au. And I just co-founded a new company.
It is a common misconception that DRBD (or any block-level data replication) solution can magically make an application crash-safe that intrinsically isn’t. Baron highlights that misconception in a recent blog post.
I want to reiterate and stress that point here: if your application can’t reliably survive a node crash, it won’t successfully fail over on a replicated (or shared, for that matter) data device. But if it can, and DRBD is replicating synchronously, then DRBD won’t break it. In other words: try pulling the power plug on your machine while your app is running, and power back on. If your application recovers to a consistent state, you’re clear. If it doesn’t, don’t bother adding DRBD until you fix that.
You must fix any layer in your stack that isn’t crash safe, if you even want to start thinking about high availability. ext2, which Baron mentions in his post, isn’t crash safe. MySQL with a database using the MyISAM storage engine isn’t crash safe. KVM with virtual block devices in
cache=writeback mode isn’t crash safe. Running on a RAID controller with the write cache enabled when its battery is dead isn’t crash safe.
And now, Windows. We have received a generous grant (from a source not wishing to have their identity disclosed in public) to fund a port to the Windows Server platform. Development work on this port has commenced back in mid-January.
So, storage and data center folks on the West Coast, come and meet us! MySQLers and Drizzlers from the Pacific Northwest (mordred, that means you!), drop us a line to see how we can link up! Novell folks, let’s sit down and chat about what we can do to help improve SLE 11 HAE! Red Hat/Fedora people, let’s talk about how we can improve DRBD integration in your distributions! Virtualization folks, let’s talk about seamless DRBD integration with libvirt, like it already exists in Xen!
Please drop us a line at
linuxcon at linbit dot com or
lpc at linbit dot com if you are coming to either event, so we can arrange a get-together. Thanks!
Logicworks, based in New York City, is a long-term enterprise user of DRBD based storage replication. If you’re into baseball and follow MLBlogs, DRBD is what it runs on and Logicworks is who runs it. Their Managed Storage Services offering has leveraged DRBD for a long time. The same is of course true for their Private Cloud service.
This is really cool stuff.