Yes. As the GP stated, all data added/updated/deleted since last snapshot will be lost. If your data is that critical you can use AOF with "appendfsync always"

Yes. As the GP stated, all data added/updated/deleted since last snapshot will be lost. If your data is that critical you can use AOF with "appendfsync always" which will fsync every write operation into a log that will replayed on startup (at a speed cost). Setting it to fsync every second (instead of always) is a good compromise.