What is Bartleby’s work performance like initially?

Initially, Bartleby was hard-working and diligent.

At first Bartleby did an extraordinary quantity of writing. As if long famishing for something to copy, he seemed to gorge himself on my documents. There was no pause for digestion. He ran a day and night line, copying by sun-light and by candle-light. I should have been quite delighted with his application, had be been cheerfully industrious. But he wrote on silently, palely, mechanically.