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web/content/posts/2023-09-12/_index.md

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+---
+title: "Update 2023-09-12"
+author: "Rodrigo Arias Mallo"
+date: 2023-09-12
+---
+
+This is a summary of notable changes introduced in the jungle cluster in the
+last months.
+
+### New Ceph filesystem available
+
+We have installed the latest [Ceph filesystem][1] (18.2.0) which stores three
+redundant copies of the data so a failure in one disk doesn't cause data loss.
+It is mounted in /ceph and available for use in the owl1, owl2 and hut nodes.
+
+[1]: https://en.wikipedia.org/wiki/Ceph_(software)
+
+The throughput is limited by the 1 Gigabit Ethernet speed, but should be
+reasonably fast for most workloads. Here is a test with dd which reaches the
+network limit:
+
+```txt
+hut% dd if=/dev/urandom of=/ceph/rarias/urandom bs=1M count=1024
+1024+0 records in
+1024+0 records out
+1073741824 bytes (1,1 GB, 1,0 GiB) copied, 8,98544 s, 119 MB/s
+```
+
+### SLURM power save
+
+The SLURM daemon has been configured to power down the nodes after one hour of
+idling. When a new job is allocated to a node that is powered off, it is
+automatically turned on and as soon as it becomes available it will execute the
+job. Here is an example with two nodes that boot and execute a simple job that
+shows the date.
+
+```txt
+hut% date; srun -N 2 date
+2023-09-12T17:36:09 CEST
+2023-09-12T17:38:26 CEST
+2023-09-12T17:38:18 CEST
+```
+
+You can expect a similar delay (around 2-3 min) while the nodes are starting.
+Notice that while the nodes are kept on, the delay is not noticeable:
+
+```txt
+hut% date; srun -N 2 date
+2023-09-12T17:40:04 CEST
+2023-09-12T17:40:04 CEST
+2023-09-12T17:40:04 CEST
+```
+
+### Power and temperature monitoring
+
+In the cluster, we monitor the temperature and the power draw of all nodes. This
+allows us to understand which machines are not being used and turn them off to
+save energy that otherwise would be wasted. Here is an example where some nodes
+are powered off to save energy:
+
+![power](./power.png)
+
+We also configured the nodes to work at low CPU frequencies, so the temperature
+is kept low to increase the lifespan of the node components. Towards these
+goals, we have configured two alerts that trigger when the CPUs of a node
+exceeds the limit temperature of 80 °C or when the power draw exceeds 350 W.
+
+By keeping the power consumption and temperatures controlled, we can safely
+incorporate more machines that will only be used on demand.