Theoretical writes/sec limit

If I have solarwinds which has an alert set whenever we have more than 300 writes per second, and I know 300 writes per second is fine, and the writes per second often goes over 6500, how can I work out what the theoretical limit of writes per second is, so I can alter the alert thus making it actionable? If "The number of writes should not exceed 85% of the disk capacity" how can I work out the number of writes that are possible with my current disk configuration?