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Downloaded bytes, host writes and NAND writes are different quantities; physical write amplification requires the last of them.
Map the cache data path
A model may pass through a downloader, temporary file, validation, decompression and final cache directory. Network volume does not automatically equal host writes: retries, transformations and reuse of existing files can change the relationship. Do not assume that moving a file rewrites all its contents without understanding the operation and filesystem. Start with a lifecycle diagram for one model revision, naming stages and owners. Record whether each stage creates a file, reuses an object or deletes an older copy. This separates unnecessary downloader work from internal SSD activity that application network statistics cannot reveal.
Read host writes with units
In the libnvme SMART reference, Data Units Written concerns data written by the host to the controller, excluding metadata. It is expressed in thousands of 512 byte units and rounded upward. Conversion must therefore respect those units; a small delta is not an exact byte measurement of one operation. It is also different from Host Write Commands, which counts commands. Preserve raw values and converted estimates separately. Zero may mean that the unit count is not reported, so it cannot automatically establish no writes. Account for controller scope and unrelated writers, or another application’s writes may be incorrectly attributed to the model.
Do not invent physical amplification
Physical write amplification relates NAND writes to host writes over comparable scope and time. Ordinary Data Units Written does not supply the numerator. If NAND vendor telemetry is absent or its meaning is unverified, leave the metric unknown. Host writes divided by downloaded bytes can describe a separate application path metric, but must not be renamed physical SSD WAF. Even available vendor fields require checks of units, scope and resets. Similar names do not make two quantities comparable. A valid calculation first explains what work each source measures, then presents the ratio and remaining measurement limitations.
Run a bounded control experiment
Choose one model revision, pin the initial cache state, limit download count and collect before and after observations. One case examines a missing cache, another verifies reuse, and a third may examine a specific update path. Exclude unrelated writes through a test environment or state them as a limitation. The fio documentation helps define a separate controlled I/O profile using a dedicated test file, but a synthetic test does not replace measuring the actual downloader. Do not run unbounded writes on operational storage to estimate wear. Preserve all settings and actual operations so reduced host writes reflect cache behavior rather than an accidentally omitted download.
Connect results to cache policy
If repeated loading still produces substantial writes, inspect revision keys, temporary directories, duplicate processes and eviction conditions. See storage optimized hosting and persistent Runpod volumes. The conclusion describes measured application writes and available SSD telemetry. It neither predicts an exact failure date nor establishes universal endurance across drive models. Cache retention decisions consider capacity, reuse frequency and recoverability. Preserving the distinction between network, host and NAND improves policy without false coefficients and shows which additional information would be required for a stronger conclusion.