## Problem
Uploading documents (especially images) to Marqo eventually started failing with a persistent 429 Too Many Requests: "Marqo-OS received too many requests! Please try reducing the frequency of add_documents and update_documents calls". Searches still worked fine. The 429s persisted indefinitely on that index no matter how long the reporter waited, even though the machine had 16 GB RAM and a 6-core CPU. The OpenSearch logs showed the real cause: the low disk watermark was exceeded, which blocks writes while reads keep working.
## Verified fix
The 429s were a symptom of a full disk: OpenSearch's DiskThresholdMonitor showed `low disk watermark [85%] exceeded`, which blocks indexing while reads keep working. Freeing disk space (the reporter had only ~17 GB free / 14.9%) resolved it. If Marqo returns persistent 429s on writes while searches work, check free disk space on the OpenSearch data volume first.
Source: https://github.com/marqo-ai/marqo/issues/358