Hi,
The HMC is an appliance device.
It can perform many tasks, both in the background and for HMC users, making changes for the sysadmin team to the 64 possible Power servers it controls.
Plus tasks for PowerVC users remotely.
Gathering stats from the hardware (hypervisor) and VIOSs for monitoring is not exactly a high priority tasks.
VIOS performance can be critical to the best performance for the VMs it serves with I/O.
Real-time stats aren't a priority compared to I/O for networks and storage.
The HMC compromise is that performance stats are collected at 5-minute intervals to keep CPU cycles within acceptable limits. I imagine the design teams are cautious in their approach.
I am not a spokesperson for the IBM HMC or VIOS teams, and the design and this information might be out of date.
If you want faster statistics, you can monitor the VIOS directly, but you'll need to ensure you don't create performance problems on the VIOS.
I hope this background information helps understanding, Nigel
Original Message:
Sent: 3/23/2026 3:33:00 AM
From: Joerg Kauke
Subject: RE: Performance metrics from your HMC to Prometheus
Hello Nigel,
thanks for sharing your deep knowledge about these metrics. It clarifies some of my confusion.
May I ask you, which API Endpoint you are using nextract plus? Is it Long Term oder PCM?
My intention was, to use the HMC data in Prometheus and trigger some alerts if thresholds are reached.
'njmon' would be the better solution, but the VIOS has a restricted network and it's difficult to get the the data out of the VIO Servers.
I will check a little further to find a way.
Many Thanks to you.
Kind regards.
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Joerg Kauke
Unix Administrator
COOP Switzerland
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Original Message:
Sent: Fri March 20, 2026 08:49 AM
From: Nigel Griffiths
Subject: Performance metrics from your HMC to Prometheus
Hi a few thoughts and places to check.
I would first check the Grafana Units used for statistics, because Bytes are a "pain in the neck" with too many digits.
Meaning the IBMi value might be in MB or KB. Even so nextract 10,700,000 / 1024 = 10,449 and not HMCi 168,000
Are the HMCi bytes actually packets? 10700000 / 168000 = 64 bytes per packet - Hmm! Plausible!
The documentation for the HMC statisitcs are here:
https://www.ibm.com/docs/en/power9/9009-22A?topic=specification-managed-system-processed-aggregated-metrics-json
nextract plus is sending the statistics "as found" in the data structure returned from the HMC i.e. Python uses the labels and values found.
The HCMi renames them vios_network_virtual_received_bytes - this could be a coding mistake. I know I do this often while rapidly hacking code.
Note: nextract refers to this statistic as vios_network_virtual_receivedBytes. So, the "receivedBytes" come from the original data structure from the HMC.
In fact, receivedBytes does not appear in the nextract code at all.
Perhaps HMCi is confused receivedBytes with receivedPackets, receivedPhysicalBytes or receivedPhysicalPackets.
That is a wild guess.
It is complicated but the bit for VIO networks is found under
"viosUtil": [{
. . .
"network": {
. . .
"virtualEthernetAdapters": [{
physicalLocation": "string", "vlanId": "number", "vswitchId": "number",
"isPortVLANID": "boolean",
"receivedPackets": ["number", "number", "number"],
"sentPackets": ["number", "number", "number"],
"droppedPackets": ["number", "number", "number"],
"sentBytes": ["number", "number", "number"],
"receivedBytes": ["number", "number", "number"],
"receivedPhysicalPackets": ["number", "number", "number"],
"sentPhysicalPackets": ["number", "number", "number"],
"droppedPhysicalPackets": ["number", "number", "number"],
"sentPhysicalBytes": ["number", "number", "number"],
"receivedPhysicalBytes": ["number", "number", "number"],
"transferredBytes": ["number", "number", "number"],
"transferredPhysicalBytes": ["number", "number", "number"] }],
I hope this helps a bit. Willing to accept the blame if it's my code that is wrong.
------------------------------
Nigel Griffiths - IBM retired
London, UK
@mr_nmon
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