I have come to the conclusion that the best data format for 'raw' scientific timeseries data is good-old, plain CSV (comma separated values):
- ➕ new data easily appendable to files
- 🔎 searchable with command-line tools (grep, sed, awk, perl, etc.)
- 📝 easily modifyable as well
- 🗜️ compresses like crazy ('xz -v -9' is insane, plain text compresses even better than already-dense binary measurement data in my experience)
- 📤 readable by any data analysis language