Mostly idle at work? Microsoft Azure has some bursty VMs it'd love to sell you

We're looking at you, accounting*

Azure Microsofties have crossed their fingers - and everything else - that Redmond's new VM family will hit the sweet spot for customers with sporadic cloud computing jobs.

Yesterday, Microsoft announced a new B-Series line of CPU virtual machines designed specifically for workloads that stay idle except for some "bursty" spikes a few times a day or a week.

Use cases would include simple websites, testing environments and small databases, such as the ones used by accounting departments.

Handling burstiness is not a new concept in the IT world: businesses have been able to kill, add or resize virtual machines in a third party's data centres (or in their own) for years.

But "the reality is that many VMs still sit idle when workload demand is low," Gartner cloud analyst Marco Meinardi told The Register. Firms typically over-provision CPUs to avoid the performance and availability issues from always resizing, such as waiting for a reboot.

Per-minute VM usage sellers such as Microsoft and Amazon realized they could offer shared CPUs at a much lower cost than normal by first guaranteeing a baseline performance. Then, as long as the workloads stayed below that, they would dish out "credits" customers can bank and use to get more performance as needed.

Competitor Amazon Web Services already offers its own VM boxes that give out credits for when your workload grunt stays below a certain baseline, called T2. Microsoft offers other flexible-sized VMs but boasts that the B-series is its cheapest offering for bursty workloads.

Aidan Finn, technical sales director for Dublin-based Azure cloud solutions provider MicroWarehouse told The Register "the B-Series is useful and it has been wanted".

He said that a customer might spend about £114 a month for an Azure F2 VM in the West Europe region with 2 vCPUs and 4GB of RAM regardless of whether it was busy or idle. But you could now get the same-sized B2S in the West Europe region for under £20 a month "if the workload is suitable".

You wouldn't want the B-series for workloads with constant medium or high CPU utilisation, he said.

Meinardi also said applications that don't allow for CPU performance variability wouldn't work optimally with the B-series, for example, apps with code written to give an error if a calculation does not arrive within a set number of seconds.

Dave Starling, CTO of Seenit, a London-based firm that develops a video collaboration tool, agreed the baseline infrastructure "isn't small or cheap to run" and the Azure B-series would be "pretty useful" for its workloads. ®

* It's not you, it's your computing workloads (that are sometimes idle)...

UPDATE: Microsoft's explained to us that "A credit is equal to one vCPU running at 100% utilization for 1 minute." As explained here, each B-series instance type generates different amounts of credits each hour. There's also a ceiling on the number of credits users can retain. The low-end single-vCPU Standard_B1s instance, for example, generates six credits an hour and has a limit of 144 credits in the bank for just under 2.5 hours of full-CPU function. The eight-vCPU Standard_B8ms instance accrues 81 credits an hour and lets you bank 1,944 in any 24 hour period.

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