Author Archives: Blair Bethwaite

Corollary of local ephemeral storage

I mentioned in the last post that the Monash NeCTAR node is using local direct-attached disk for instance ephemeral storage, but I forgot to expand on the caveats, so here goes:

It’s important to note that this means loss or failure of a hypervisor/compute-node could mean loss of the ephemeral storage of instances on that node at the time, depending on the severity of the failure. In many cases we’ll be able to restart and recover these instances later (of course memory state is gone), but how long that will take depends on the failure, so ephemeral storage availability in the face of hardware issues is unpredictable versus other NeCTAR nodes using shared storage who can (given available time and resources) more readily attempt recovery. However, this is cloud computing roughly mimicking the model pioneered by EC2, so really, just don’t rely on ephemeral storage to hold anything you can’t easily recompute or aren’t readily backing up to persistent storage – and go backup your laptop while you’re thinking about it!

Persistent block storage (aka volumes) will make an appearance on the Monash node soon (hopefully a generally available pre-production service before end of July). University of Melbourne should have theirs in production within a few weeks. So, stay tuned…

R@CMon Phase 1 is go!

Two weeks ago the first phase of the Monash node of the NeCTAR RC (Research Cloud) went live to public (yes, this post is late!). If you’re a RC user you can now select the “monash” cell when launching instances. If you’re not already using the RC then what are you waiting for?! Get to and spin up your first server.

You can launch instances to the Monash node via the Dashboard (see pic), through the OS API by specifying either a scheduler hint “cell=monash”, or via the EC2 API specifying availability-zone=”monash”. Those last two instructions are likely to evolve with future versions of the APIs so stay tuned to (and search for “cells”) for current instructions.


A bit of background about Monash phase 1.

There’s about 2.3k cores available in the current deployment – phase 2 will more than double this. The hypervisors are running Ubuntu 12.04 LTS on AMD6234 CPUs with 4GB RAM per core.

What’s different from the other NeCTAR RC nodes?

The instance associated ephemeral storage is delivered by a local RAID10 on each hypervisor (as opposed to a pool of shared storage, e.g., NFS share) with live-migration possible thanks to KVM’s live block migration feature (anybody interested should note that block migration is replaced with live block streaming in the upstream QEMU code). This means ephemeral storage performance actually scales as you add instances, more or less predictably subject to activity from co-located guests. As OpenStack incorporates features to limit noisy neighbour syndrome we’ll be able to take full advantage of those too.

We pass host CPU information from the host through libvirt to the guests to give best performance possible to code that can make use of it.

Who built it?

Thanks goes to a big team both here at Monash across MeRC (the Monash eResearch Centre) and eSolutions (Monash’s central ICT provider), and also the folks at NeCTAR and the NeCTAR lead node at University of Melbourne. Of course it wouldn’t have been possible without OpenStack and the community of contributors around it, so thanks all!