After our hugely successful summer class in Silicon Valley, we have set up a survey to help us determine the location of our Q4 DRBD Total course in the United States. So let us know where you would like to see the next incarnation of the industry’s premier Linux High Availability training!
Our survey just takes a minute to complete. We appreciate your input!
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Posted by Florian Haas
Neither is ext3. Nor ext4. Nor btrfs. And thus, none of these will work on dual-Primary DRBD. Nor active-active shared storage. Nor any synchronously replicated active-active SAN. And we’re telling you very clearly.
So if you choose to ignore all warnings and put ReiserFS on dual-Primary DRBD, and mount it from two nodes, you’ve just signed up for wrecking your data. And when that happens, don’t come whining. And don’t blame DRBD or any other of the technologies you may be choosing to employ while ignoring the documentation.
7 Comments | Rant | Permalink
Posted by Florian Haas
This year’s Linux Plumbers Conference is taking place November 3-5, in Cambridge, MA, United States. The CfP is already closed and the program is due any day now, but the co-located miniconference on high availability clustering is still accepting proposals. This is your chance to get involved!
So if you plan to attend Plumbers or just happen to be in the area, please submit your talk! Miniconference talks are not expected to be full-blown presentations. Instead, you can float an idea in just a 5-10 minute talk and then stimulate a vibrant group discussion.
Even if you are not attending, you can still help! We are always eager to hear from our user community. What HA problems are you currently facing that the existing Linux clustering stack does not solve? How well does your application integrate with HA? Where can we improve? What’s already good, and can be made better? What sucks?
Feel free to comment below. Or send us an email on one of the mailing lists. Or grab us in #linux-ha or #linux-cluster on freenode. Make yourself heard!
Leave a Comment » | Conferences, Corosync, Heartbeat, Linux-HA | Permalink
Posted by Florian Haas
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.
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.
5 Comments | MySQL, Storage, Virtualization | Permalink
Posted by Florian Haas
We usually do our English-language Linux Cluster Stack training sessions in the U.S., with training in Europe being primarily held in German. So if you live in Europe, speak English, and want to hone your high availability skills on your own continent, learning from the top notch experts, here is your rare chance:
November 9-12, were are doing our DRBD Total training in one of Europe’s finest cities, Berlin. Berlin is easily reached by air or rail, and our training location is directly next to historical Allied Checkpoint Charlie on Friedrichstraße. Training is exclusively in English, and covers DRBD, the Heartbeat/Corosync/Pacemaker cluster stack, and a number of high availability applications.
I hear you say, “November? Then why are you telling me this now?” Well guess what, there is a 15% early bird discount off the standard price if you register before August 31. So register quickly and grab your chance! Our classes usually sell out fast.
By the way: if you do speak German, we also have a German-language training coming up in Vienna in September. Take a look!
