Add web post update for 2025

Reviewed-by: Aleix Boné <abonerib@bsc.es>

web/content/posts/2025-09-26/_index.md

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+---
+title: "Update 2025-09-26"
+author: "Rodrigo Arias Mallo"
+date: 2025-09-26
+---
+
+This is a summary of notable changes introduced in the last two years. We
+continue to maintain all machines updated to the last NixOS release (currently
+NixOS 25.05).
+
+### New compute node: fox
+
+We have a new [fox machine](/fox), with two AMD Genoa 9684X CPUs and two NVIDIA
+RTX4000 GPUs. During the last months we have been doing some tests and it seems
+that most of the components work well. We have configured CUDA to use the NVIDIA
+GPUs, as well as AMD uProf to trace performance and energy counters from the
+CPUs.
+
+### Upgraded login node: apex
+
+We have upgraded the operating system on the login node to NixOS, which now runs
+Linux 6.15.6. During the upgrade, we have detected a problem with the storage
+disks. The `/` and `/home` partitions sit on a
+[RAID 5](https://en.wikipedia.org/wiki/Standard_RAID_levels#RAID_5),
+transparently handled by a RAID hardware controller which starts its own
+firmware before passing the control to the BIOS to continue the boot sequence. A
+problem during the startup of the firmware prevented the node to even reach the
+BIOS screen.
+
+After a long debugging session, we detected that the flash memory that stores
+the firmware of the hardware controller was likely to be the issue, since
+[memory cells](https://en.wikipedia.org/wiki/Flash_memory#Principles_of_operation)
+may lose charge over time and can end up corrupting the content. We flashed
+the latest firmware so the memory cells are charged again with the new bits and
+that fixed the problem. Hopefully we will be able to use it for some more years.
+
+The SLURM server has been moved to apex which allows users to also submit jobs
+to fox.
+
+### Migrated machines to BSC building
+
+The server room had a temperature issue that had been affecting our machines
+since the end of February of 2025. As the summer approached, the temperature
+exceeded the safe limits for our hardware, so we had to shutdown the cluster.
+
+![Room temperature](temp.png)
+
+Since then, we have moved the cluster to BSC premises, where it now rests at a
+stable temperature, so hopefully we won't have more unscheduled downtime.