Built to Be Efficient

Built to Be Efficient

Device Sentinel watches every device in your home and remembers what it learns, which means it writes to disk. On a machine with an SSD the cost is negligible. On a Raspberry Pi running from an SD card, repeated small writes are among the few things that genuinely shorten the life of the hardware, so the integration's storage design treats write volume as a constraint rather than an afterthought. This page describes how that works and which settings matter if your storage is the fragile kind.

How the Integration Manages Its Writing

Storage is divided between two files according to how often the data changes. A small file carries the per-device values that move whenever a device reports, such as the activity clock and current signal reading, while a large file carries everything learned over time: the daily history, the verdicts, the problem list, and the recent incident and silence records. Because a device reporting normally only touches the small file, the large one is spared the churn of ordinary activity entirely.

Routine changes are also coalesced rather than written as they occur. When a device reports and its clock advances, that change is held in memory and saved together with everything else that accumulated during the storage write interval, on a single schedule. The large file is written on that same schedule, and only when something worth keeping has happened since its last write, so on a settled system it is touched a handful of times a day.

Coalescing never applies to anything a restart must not lose. A device going silent, a battery crossing your threshold, an item added to or checked off the problem list: these are written to both files the moment they happen, and both files are written once more at every clean shutdown. The exposure in a power cut is therefore limited to at most one interval of routine clock progress, which repairs itself as each device reports again.

The four Markdown reports are written at startup, at midnight, at your daily brief time, and when you press the Regenerate Reports button, never continuously in the background.

The Settings That Govern It

Both are on the [Advanced](Advanced) screen. The storage write interval, five to sixty minutes with a default of fifteen, sets how long routine changes are held before being saved; a longer interval means fewer writes in exchange for slightly more of the self-repairing clock data at risk during a power cut, and it is the most effective single adjustment if write volume concerns you. How much history to keep, thirty days to a year with a default of ninety, determines how many days of per-device daily history are retained and therefore how large the big file eventually grows.

For an SD card installation, a thirty-minute interval with the default history is a sensible pairing. On an SSD the defaults are fine and the subject needs no further thought.