I like this image of the Windows storage driver stack.

https://i-technet.sec.s-msft.com/dynimg/IC347746.gif

The allocation unit is an attribute of the filesystem, governing initial the incremental filegrowth possible.

Although its old, I like...

Unless a test stresses the metadata differences or potential file interleave/contiguity differences between 4k and 64k au, I'd expect no measurable difference in a disk IO test.

For example, with a...

The allocation unit size has much less effect on size of SQL Server IO than is commonly believed.

Consider writes to the transaction log. Each write is a minimum of 512bytes...

What is the transaction log setup like? EG each txlog on its own LUN, or do any of the txlogs share with other files?

There are 128 transaction log buffers...

We've watched trace flag 8048 go into numerous systems now, and have not observed any negative effects. We've been watching stolen memory, all waits and spinlocks in 5 minute...