SOLVED: What is Different About an Azure B-Series Virtual Machine?

Put simply, Azure B Series virtual machines will only operate at about 1/3rd of their CPU potential most of the time.

Microsoft recommends B-Series for “burst” workloads, and not continuous loads and they make that work using a credit system to stop these VM’s from hogging the CPU.

For instance a common B-Series Azure Machine Size is “Standard_B8ms” which under normal conditions, the CPU max’s at 33% (i.e. ROUGH equivalent of 2.7 cores in an 8 core VM) but can burst to 100% until its credits run out causing it to slow back to 33% for at least 1 hour.

Notably, credits reset to zero after every reboot, start adding to the credit bank immediately on power up, and max out after 24 hours (see table below for details).

This makes B-Series VM’s good for services that get busy periodically but often slow back down. In most companies, this would include Domain Controller VM’s, Print Servers, File Servers and low use FTP servers.

EXAMPLES OF AZURE B-SERIES IN ACTION

Lets look at one example using two different B Series Burstable Virtual Machine Sizes.

SCENARIO

• Perhaps you have a backup server that only works hard overnight
• If that VM was physical your backup program (Veeam, BackupExec, Microsoft Azure Backup…) would need to run at 100% on 10 cores for 12 hours
• You rebooted the Azure VM and waited 5 hours to start the app

$266/month 8core/32GB B Series

• The server would start with 325 credits (81 x 5)
• it would run for 5 hours at 100% CPU speed, then 33% for 1 hour
• then 100% CPU for 1 hour, then 33% for 1 hour
• then 100% CPU for 1 hour, then 33% for 1 hour
• then 100% CPU for 1 hour, then 33% for 1 hour
• then 100% CPU for 1 hour, then 33% for 1 hour
• then 100% CPU for 1 hour, then 33% for 1 hour
• making the total time 16 hours

$400/month 12core/48GB B Series

• The server would start with 605 credits (121 x 5)
• it would run for 5 hours at 100% CPU speed, then 33% for 1 hour
• then 100% CPU for 1 hour, then 36% for 1 hour
• then 100% CPU for 1 hour, then 36% for 1 hour
• then 100% CPU for 1 hour, then 36% for 1 hour
• then 100% CPU for 45 minutes

ALTERNATIVE TO AZURE B-SERIES

You could use an Azure D-Series Gen 5 Size for $570/month and get 8 cores with 32GB of memory that you can run full tilt all day and all night. This is the least cost option if the the server’s cores are busy all the time.

WHAT PHYSICAL CPU’s DOES AZURE B-SERIES USE

This is a difficult question to answer because Microsoft using servers with CPU’s that were released in 2014 all the way through to CPU’s released in 2020. As of January 2024 here is the list of CPU’s you could get assigned to you if you use Azure B Series:

• 3rd Generation Intel® Xeon® Platinum 8370C (Ice Lake)
• Intel® Xeon® Platinum 8272CL (Cascade Lake)
• Intel® Xeon® 8171M 2.1 GHz (Skylake)
• Intel® Xeon® E5-2673 v4 2.3 GHz (Broadwell)
• Intel® Xeon® E5-2673 v3 2.4 GHz (Haswell)

OTHER NOTABLE B-SERIES LIMITATIONS

The Azure B Series Size VM’s do NOT support Nested Virtual Machines, only have a few versions that allow Accelerated Networking, and the bottom level “B1” is only supported on Linux deployments.

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