Re: [PATCH] blk-settings: round down io_opt to at least 4K

[Mikulas Patocka]

On Mon, 3 Feb 2025, Martin K. Petersen wrote:

> 
> Hi Mikulas!
> 
> > The purpose of this patch is to avoid doing I/O not aligned on 4k 
> > boundary.
> >
> > The 512-byte value that some SSDs report is just lie.
> 
> So is 4K, though.

Do you think that SSDs benefit from more alignment than 4K?

Based on my understanding (and some IOPS testing), SSDs have a remapping 
table that maps every 4K block to the physical location. So, 8K (or 
larger) I/Os don't have higher IOPS than 4K I/Os.

2K and smaller I/Os have worse IOPS than 4K I/Os, because they perform 
read-modify-write cycle.

If you have some SSD that has higher IOPS with alignment larger than 4K, 
let me know.

Mikulas