This blog contains experience gained over the years of implementing (and de-implementing) large scale IT applications/software.

Tag: aem

HowTo: Install Azure Enhanced Monitoring for Linux for SAP

One SAP support prerequisite for running SAP on Azure, is that you must have Azure Enhanced Monitoring for Linux installed onto the Azure Linux VMs where your SAP application runs (including DB servers). Details are in SAP note 2015553.

In this brief post I show how to check if it is already installed, then how to install it, without needing to install the Powershell Azure Cmdlets.

What is Azure Enhanced Monitoring for Linux?

Azure Enhanced Monitoring for Linux (AEM) is an Azure VM extension installed onto the target Linux VM.
The extension uses the Azure Instance Agent to pull additional telemetry information down onto the local VM, and places it into a file on the Linux file system called /var/lib/AzureEnhancedMonitor/PerfCounters.

This special file is pure ASCII text with data inside that is semi-colon separated.
You can use Linux command line utilities to query information from the file (it’s readable by any user).

The file is parsed by the SAP Host Agent (also installed on every SAP VM) and made available in the monitoring memory segment used by the Netweaver ABAP stack, with the data being visible in transaction ST06 (OS06).

How to Check if AEM Is Installed

There are a number of ways to check if Azure Enhanced Monitoring for Linux is installed on a VM:

  • Inside the VM in Linux we can check for the existence of file: “/var/lib/AzureEnhancedMonitor/PerfCounters”
  • Inside the VM in Linux we can check the extension home dir exists: “/var/lib/waagent/Microsoft.OSTCExtensions.AzureEnhancedMonitorForLinux-*”
  • In the Azure Portal, we can check the status of the extension in the Azure Portal:
  • In the Azure Cloud Shell, we can either Test or Get the AEM Extension to see if it is installed:
Get-AzVMAEMExtension -ResourceGroupName <RG-NAME> -VMName <VM-Name>
Test-AzVMAEMExtension -ResourceGroupName <RG-NAME> -VMName <VM-Name>

Installing AEM

There are two ways to install the Azure Enhanced Monitoring for Linux extension into a VM:

  • Using local PowerShell (on your computer) with the Azure Cmdlets installed.
    You will need to have the rights on the local machine to perform the install of the Azure Cmdlets.
    I will not cover this method as it is quite tedious to setup and the chances are that your PowerShell is locked down by your company and will not allow you to install the required Cmdlets.
  • Using Powershell in the Azure Portal Cloud Shell.
    This has all the required Cmdlets already installed, but to setup the Cloud Shell you will need rights in Azure to be able to create a Storage Account to use for your shell home location.

Out of the two options, I usually opt for the Cloud Shell. Once you have it setup, you will find you can use it for many other things and access it from anywhere!
In this post I will be using Cloud Shell to do the installation.

To install the AEM extension, we use Powershell commands to do the following sequence of tasks:

  • Obtain our subscription context.
  • Deploy the extension to the specific VM in the subscription.

Let’s start the Cloud Shell (NOTE: You will need a Storage Account for the Cloud Shell to work).
Go to the Azure Portal and click the button on the button bar:

Make sure that you are in a PowerShell Shell:

We may need to switch to a specific subscription.
We can list all subscriptions by calling Get-AzSubscription and filtering on the Id property:

Get-AzSubscription | Select-Object Id

We can then set the context of our Cloud Shell to the specific subscription Id as follows:

$context = Get-AzSubscription -SubscriptionId '<SubscriptionID>'
Set-AzContext -SubscriptionObject $context

Once the code has executed, we can check if the AEM extension is already installed:

Get-AzVMAEMExtension -ResourceGroupName <RG-NAME> -VMName <VM-Name>

If the AEM extension is already installed, then we will see output being returned from the Get command:

ResourceGroupName       : UK-West
VMName                  : vm01
Name                    : AzureEnhancedMonitorForLinux
Location                : ukwest
Etag                    : null
Publisher               : Microsoft.OSTCExtensions
ExtensionType           : AzureEnhancedMonitorForLinux
TypeHandlerVersion      : 3.0
Id                      : /subscriptions/mybigid/resourceGroups/UK-West/providers/Microsoft.Compute/virtualMachines
                          /vm01/extensions/AzureEnhancedMonitorForLinux
PublicSettings          : {
                            "cfg": [
                              {
                                "key": "vmsize",
                                "value": "Standard_D4s_v3"
                              },
                              {
                                "key": "vm.role",
                                "value": "IaaS"
                              },
                              {
                                "key": "vm.memory.isovercommitted",
                                "value": 0
                              },
                              {
                                "key": "vm.cpu.isovercommitted",
                                "value": 0
                              },
                              {
                                "key": "script.version",
                                "value": "3.0.0.0"
                              },
                              {
                                "key": "verbose",
                                "value": "0"
                              },
                              {
                                "key": "href",
                                "value": "http://aka.ms/sapaem"
                              },
                              {
                                "key": "vm.sla.throughput",
                                "value": 96
                              },
                              {
                                "key": "vm.sla.iops",
                                "value": 6400
                              },
                              {
                                "key": "wad.isenabled",
                                "value": 0
                              }
                            ]
                          }
ProtectedSettings       :
ProvisioningState       : Succeeded
Statuses                :
SubStatuses             :
AutoUpgradeMinorVersion : True
ForceUpdateTag          : 637516905202791108
EnableAutomaticUpgrade  :


If the AEM extension is not installed, not output will be seen from the “Get” command.
We can then install the AEM extension with the “Set-AzVMAEMExtension” command as follows:

Set-AzVMAEMExtension -ResourceGroupName <RG-NAME> -VMName <VM-Name>

The extension should be installed successfully.
If you need to remove it, you can use the “Remove-AzVMAEMExtension” command.

There is a “Test” command that you can call to test the AEM:

Test-AzVMAEMExtension -ResourceGroupName <RG-NAME> -VMName <VM-Name>

Finally, if you want to see the additional command line options, then use the standard “Get-Help” as follows:

Get-Help Set-AzVMAEMExtension -Full

Issues with AEM

There’s one known issue with Azure Enhanced Monitoring for Linux, the number of data disks reported in the PerfCounters file seems to be limited to 9.
This means that if you have more than 9 data disks, the performance data may not be visible in the file and therefore not visible in SAP.
It’s possible a fix is on the way.

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Checking Azure Disk Cache Settings on a Linux VM in Shell

In a previous blog post, I ended the post by showing how you can use the Azure Enhanced Monitoring for Linux to obtain the disk cache settings.
Except, as we found, it doesn’t easily allow you to relate the Linux O/S disk device names and volume groups, to the Azure data disk names.

You can read the previous post here: Listing Azure VM DataDisks and Cache Settings Using Azure Portal JMESPATH & Bash

In this short post, I pick up where I left off and outline a method that will allow you to correlate the O/S volume group name, with the Linux O/S disk devices and correlate those Linux disk devices with the Azure data disk names, and finally, the Azure data disks with their disk cache settings.

Using the method I will show you, you will see how easily you can verify that the disk cache settings are consistent for all disks that make up a single volume group (very important), and also be able to easily associate those volume groups with the type of usage of the underlying Azure disks (e.g. is it for database data, logs or executable binaries).

1. Check If AEM Is Installed

Our first step is to check if the Azure Enhanced Monitoring for Linux (AEM) extension is installed on the Azure VM.
This extension is required, for your VM to be supported by SAP.

We use standard Linux command line to check for the extension on the VM:

ls -1 /var/lib/waagent/Microsoft.OSTCExtensions.AzureEnhancedMonitorForLinux-*/config/0.settings

The listing should return at least 1 file called “0.settings”.
If you don’t have this and you don’t have a directory starting with “Microsoft.OSTCExtensions.AzureEnhancedMonitorForLinux-“, then you don’t have AEM and you should get it installed following standard Microsoft documentation.

2. Get the Number of Disks Known to AEM

We need to know how many disks AEM knows about:

grep -c 'disk;Caching;' /var/lib/AzureEnhancedMonitor/PerfCounters

3. Get the Number of SCSI Disks Known to Linux

We need to know how many disks Linux knows about (we exclude the root disk /dev/sda):

lsscsi --size --size | grep -cv '/dev/sda'

4. Compare Disk Counts

Compare the disks quantity from AEM and from Linux.  They should be the same.  This is the number of data disks attached to the VM.

If you have a lower number from the AEM PerfCounters file, then you may be suffering the effects of an Azure bug in the AEM extension which is unable to handle more than 9 data disks.
Do you have more than 9 data disks?

At this point if you do not have matching numbers, then you will not be able to continue, as the AEM output is vital in the next steps.

Mapping Disks to the Cache Settings

Once we know our AEM PerfCounters file contains all our data disks, we are now ready to map the physical volumes (on our disk devices) to the cache settings. On the Linux VM:

pvs -o "pv_name,vg_name" --separator=' ' --noheadings

Your output should be a list of disks and their volume groups like so (based on our diagram earlier in the post):

/dev/sdc vg_data
/dev/sdd vg_data

Next we look for a line in the AEM PerfCounters file that contains that disk device name, to get the cache setting:

awk -F';' '/;disk;Caching;/ { sub(/\/dev\//,"",$4); printf "/dev/%s %s\n", tolower($4), tolower($6) }' /var/lib/AzureEnhancedMonitor/PerfCounters

The output will be the Linux disk device name and the Azure data disk cache setting:

/dev/sdc none
/dev/sdd none

For each line of disks from the cache setting, we can now see what volume group it belongs to.
Example: /dev/sdc is vg_data and the disk in Azure has a cache setting of “none”.

If there are multiple disks in the volume group, they all must have the same cache setting applied!

Finally, we look for the device name in the PerfCounters file again, to get the name of the Azure disk:

NOTE: Below is looking specifically for “sdc”.

awk -F';' '/;Phys. Disc to Storage Mapping;sdc;/ { print $6 }' /var/lib/AzureEnhancedMonitor/PerfCounters

The output will be like so:

None sapserver01-datadisk1
None sapserver01-datadisk2

We can ignore the first column output (“None”) in the above, it’s not needed.

Summary

If you package the AEM disk count check and the subsequent AEM PerfCounters AWK scripts into one neat script with the required loops, then you can get the output similar to this, in one call:

/dev/sdd none vg_data sapserver01-datadisk2
/dev/sdc none vg_data sapserver01-datadisk1
/dev/sda readwrite

Based on the above output, I can see that my vg_data volume group disks (sdc & sdd) all have the correct setting for Azure data disk caching in Azure for a HANA database data disk location.

Taking a step further, if you have intelligently named your volume group names, you then also check in your script, the cache setting based on the name of the volume group to determine if it is correct, or not.
You can then embed this validation script into a “custom validation” within SAP LaMa and it will alert you automatically if your VM disk cache settings are not correct.

You may be wondering, why not do all this from the Azure Portal?
Well, the answer to that is that you don’t know what Linux VM volume groups those Azure disks are used by, unless you have tagged them or named them intelligently in Azure.

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