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Raspberry Pi in the datacenterSafety-critical control74

Raspberry Pi in the datacenter [/ˈræzˌbɛri ˈpaɪ ɪn ðə ˈdatasenter/] n - A Raspberry Pi is a small, ARM-born Linux computer that costs less than a dinner and draws less than a phone’s charger. In a data center this makes it fit for work that will not justify a full server yet wants a true operating system: reading sensors, logging to a time-series database, serving a small web interface, or bridging an old serial bus onto the network.

Wherein It Serves

  • Sensor aggregation. [/ˈsɛnsɒr ˈæggrɛgætɪɒn/] n A Pi can read a cluster of Temperature sensors, door contacts, or fan tachometers and publish them over MQTT or SNMP to the monitoring platform.
  • Protocol translation. [/ˈprɒtɒkɒl ˈtrænslætɪɒn/] n With a USB-to-RS-485 adapter, a Pi can speak Modbus to a legacy chiller and offer the data forth again as JSON over Ethernet.
  • Local dashboards. [/ˈlɒkæl ˈdæshbɒærds/] n A Pi with a small screen can show rack status, a countdown to the next generator test, or the present Power usage effectiveness estimate.
  • Controlled outlets. [/ˈkɒntrɒllɛd ˈæʊtlɛts/] n A Pi driving a relay board can power-cycle a stuck device from afar, provided the safety and the isolation are thought through first.

Wherein It Does Not

  • High availability. [/ˈhɪgh ˈævæɪlæbɪlɪti/] n A Pi bears a single SD card, no redundant power, and no out-of-band management. If it stands in the critical path, it wants a backup or a plan for failover.
  • High bandwidth. [/ˈhɪgh ˈbændwɪdth/] n The Ethernet shares its bus with the USB on most models. A Pi is no switch, no firewall, no packet-capture appliance.
  • Safety-critical control. [/ˈsæfɛtikrɪtɪkæl ˈkɒntrɒl/] n To drive a relay that switches mains voltage is no beginner’s undertaking. Mains-side work belongs to qualified electricians and approved equipment.

Of Making It Reliable

A Pi most oft fails at the SD card. Industrial storage, a read-only root filesystem, and the shipping of logs to a central host avail greatly; so do a sound enclosure, strain relief upon the cables, and a label declaring whose it is and why it stands there.

See On the Making of Bespoke Devices for the full road from notion to deployed instrument, and Bespoke Devices for the Datacenter for the broader matter.

Related hardware notes: Arduino, Single-board computer, Temperature sensor, Current transformer, and Power over Ethernet.

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