I’m speaking at Percona Live, LinuxCon Europe, and linux.conf.au. And I just co-founded a new company.
Roll Your Own Cloud (from linux.conf.au 2011)
February 4, 2011At linux.conf.au 2011 in Brisbane, I had the honor of co-presenting a talk on Rolling Your Own Cloud with SUSE’s Tim Serong. Take a look!
No, DRBD doesn’t magically make your application crash safe
August 17, 2010It 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.
Thus, if you want high availability, use ext3. Or ext4. Or any journaling file system. Use InnoDB for MySQL. Use cache=none
for KVM. And check those batteries. It’s that simple.
April Fool
April 1, 2010It’s coming: DRBD for Windows
April 1, 2010Unnoticed by many, DRBD ports have been spreading for some time on non-Linux platforms. AVS for (Open-)Solaris has been around for a while, and HAST for FreeBSD joined the club last autumn.
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.